delivered the opinion of the court:
Following a hearing in the circuit court of Sangamon County, respondent was involuntarily admitted to a mental health facility pursuant to sections 3 — 700 through 3 — 819 of the Mental Health and Developmental Disabilities Code (Ill. Rev. Stat. 1983, ch. 911/2, pars. 3 — 700 through 3 — 819). The court found that respondent was a person subject to involuntary admission because she was mentally ill and, because of her illness, she was reasonably expected to inflict serious physical harm upon herself or another in the near future. (Ill. Rev. Stat. 1983, ch. 911/2, par. 1 — 119(1).) The court ordered that respondent be hospitalized at St. John’s Hospital in Springfield. Respondent now appeals, contending that the State failed to prove that she was a person subject to involuntary admission.
Two petitions for involuntary admission were filed on September 10, 1984, alleging that respondent was mentally ill and that, because of her illness, she was reasonably expected to inflict serious harm upon herself or another in the near future. The petitions were accompanied by the necessary physician’s certificates stating that respondent was a person subject to involuntary admission. See Ill. Rev. Stat. 1983, ch. 911/2, par. 3-702.
A hearing on the petitions was held on September 14, 1984. Respondent’s mother testified that respondent had lived with her from 1980 until August 1, 1984. She stated that respondent had recently passed an examination which qualified her as a certified public accountant (C.RA.). In August respondent moved to her own apartment. Her mother testified that she visited respondent on September 9, 1984, and found her to be “not as well kept.” At that time respondent was “running up and down the stairs.” Later an ambulance and police arrived, and respondent was taken to St. John’s Hospital.
Dr. Philip Bornstein, a psychiatrist, testified that he examined the respondent on September 10, 1984, and found her to be restless, irritable, and hostile at the beginning of the interview. She later “settled *148down,” although Dr. Bornstein perceived her as “rather threatening.” Respondent insisted that there was nothing wrong with her, that she did not need to be in the hospital, and that she was going to call a lawyer. She remained uncooperative in subsequent interviews.
Dr. Bornstein then examined certain letters which respondent had recently mailed to Mr. and Mrs. Loren Payne. He characterized one such letter, marked as exhibit No. 5b, as essentially incomprehensible and typical of manic thinking. He described another letter, exhibit No. 9, as a compilation of disorganized thoughts suggestive of delusional thinking. He then stated:
“I think Joanna could be dangerous to others, possibly to herself if she’s depressed, but she isn’t right now but to others simply because she’s so disorganized in her thinking and apparently has a number of delusions behind her thinking which she is not able at the present time at least to share with me which are alluded to in her letters. There is a consistent thread throughout the letters, her relationship to movie stars, the F.B.I., things of this nature which she obviously feels very strongly about.
* * *
The number of illusions [sic] to last chance which I wonder if were threats or not, but most of this represents what I’m fairly certain are delusional thinking of some kind which I can’t delineate further since she hasn’t been willing to talk with me about this. I think if she has these delusions about people who are real and I noticed that all these letters are addressed to the same persons, namely, the Paynes, whoever they may be, I’ll be concerned that perhaps she has some delusions about them which would lead to their harm.”
Respondent then testified that she had become a certified public accountant on July 31, 1984. She stated that she had become acquainted with Loren Payne through telephone conversations in the course of a business relationship that had ended three years ago. She began sending Payne and his wife letters in August 1984 because she “was worried about his welfare.” She apparently feared that he had become involved in an alleged embezzlement scheme with her sister.
Respondent knew the license plate numbers of the Paynes’ cars. She stated that she had seen Mrs. Payne driving between Rochester and Springfield, Illinois. However, she denied that she had followed Mrs. Payne through Springfield as alleged by Mrs. Payne in the petition for involuntary admission. Respondent hoped that she would not see Mrs. Payne’s car again.
*149The circuit court found that the evidence established that respondent was suffering from a mental illness. Based upon Dr. Bornstein’s observations and opinion, the court found that, by reason of her illness, respondent was reasonably expected to inflict serious physical harm upon herself or another in the near future. The court then ordered that she be hospitalized. Respondent filed timely notice of appeal.
Section 1 — 119(1) of the Mental Health and Developmental Disabilities Code (Ill. Rev. Stat. 1983, ch. 91 1/2, par. 1 — 119(1)) provides that a person is subject to involuntary admission if he is mentally ill and, because of his illness, is reasonably expected to inflict serious physical harm upon himself or another in the near future. Respondent does not dispute the court’s finding of mental illness here. However, she does argue that it was not sufficiently established that she was reasonably expected to inflict serious physical harm upon herself or another in the near future. We disagree.
In a proceeding for involuntary commitment under the Act, the State is required to prove the necessary allegations of the petition by evidence, when it is all considered, that is clear and convincing. (In re Stephenson (1977), 67 Ill. 2d 544, 367 N.E.2d 1273.) However, the reviewing court must give deference to the trial court’s decision and cannot set that decision aside because it, applying the above standard, would have ruled differently. In re Johnston (1983), 118 Ill. App. 3d 214, 454 N.E.2d 840.
Here, the only evidence introduced by the State which tended to prove that respondent could reasonably be expected to harm herself or another in the near future was the testimony of Dr. Bornstein and the letters written by the respondent to the Paynes. Dr. Bornstein testified that respondent could be a danger to herself if she were depressed. However, she was not depressed at the time. He also stated that respondent “could” be dangerous to others because of her disorganized and delusional thinking. He was concerned that “perhaps” she had some delusions about the Paynes which would lead to their harm. However, because respondent refused to talk to him, Dr. Born-stein was not sure what her delusions were actually about.
In the case of In re Gregorovich (1980), 89 Ill. App. 3d 528, 411 N.E.2d 981, evidence of bizarre conduct on the part of respondent, which included the making of threats and assaults in response to her mother’s demands and the testimony of a psychiatric resident that there “is a possibility [the respondent] could harm someone,” was held to be sufficient to support, on appeal, a trial court’s finding that a mentally ill person was subject to involuntary commitment on the *150basis of the danger that she could harm someone. (89 Ill. App. 3d 528, 532, 411 N.E.2d 981, 984.) Here, the expert’s prognosis had the same degree of certainty as that in Gregorovich. The uncertainty arose partly because the respondent would be likely to be dangerous only when she was in a depressive phase of her illness. That could happen at any time without substantial warning. Courts recognize that medical experts have difficulty in predicting with certainty the likelihood that a mentally ill person will harm someone. The State is not required to wait until the danger is acute that harm may be imposed on another. In re Johnston (1983), 118 Ill. App. 3d 214, 454 N.E.2d 840.
The respondent relies on the case of In re Dieter (1977), 55 Ill. App. 3d 7, 370 N.E.2d 84, where the evidence was held to be insufficient to support a determination that the respondent there would be reasonably expected to harm herself or others. The respondent was shown to have scratch marks on her wrist, but in testimony the appellate court described as being undisputed, the respondent claimed that she received those wounds as a result of scratches by her cat. A psychiatrist had testified that she was more likely than not to harm herself or another but was unable to give reasons for his opinion. Here, there was an undisputed record of prior conduct by the respondent of delusional thinking and her letters to the Paynes. The psychiatrist who testified in regard to respondent’s condition took those matters into consideration in forming his opinion. Thus, the proof here was considerably stronger than in Dieter.
We affirm the order of commitment.
Affirmed.
McCullough, j., concurs.