Interferon alfa has antiviral, anti-proliferative and immunomodulatory effects. Treatment with interferon is related to many psychiatric side effects like depression, depressive mood, suicidal thoughts, irritability, tiredness, cognitive impairment, mania and psychosis 1. These psychiatric side effects are related to duration and dose, and when severe, usually lead to discontinuation of interferon treatment. CASE Our case study is a 17-year-old male patient. Due to frequent crying, suicidal thoughts and feelings of guilt, he was hospitalized. He had been diagnosed with chronic hepatitis B four months previously, and had been receiving 30 MIU interferon alfa 2b three times a week plus 100 mg lamivudine. Depressive symptoms like lack of interest and mental dullness began after 8 weeks of treatment. On psychiatric examination, he showed slumped posture, dullness and slowed speech. Thought content included delusions of being harmed and guilt. His affect was depressed and sometimes dysphoric. He showed decreased appetite and sleep and slowed psychomotor activity. Routine hematological and biochemical test results were normal. His cranial MR and EEG revealed no pathology. On the first day of his hospitalization, interferon and lamivudine treatment were discontinued. The patient was diagnosed with depressive d i s o r d e r w i t h p s y c h o t i c f e a t u r e s , a n d escitalopram 10 mg and risperidone 3 mg p.o. were started. When the patient developed incontinence and rigidity, the risperidone was discontinued and biperiden and lorazepam were started. During the first week of hospitalization, signs of parkinsonism disappeared and 5 mg olanzapine was started for psychotic symptoms while escitalopram 10 mg was continued. Due to extrapyramidal symptoms from the olanzapine, the drug was discontinued. In the second week of hospitalization, psychotic symptoms continued, and aripiprazole 5 mg per day was given. No side effects were observed during the 3 rd