Objectives: The aim of this study was to evaluate the outcome of a group of patients with bipolar I disorder admitted to Roozbeh Hospital, Tehran, Iran, during one year follow up. Method: In this prospective naturalistic study, 131 subjects with bipolar I disorder who were con-secutively admitted to the hospital were enrolled. Patients were assessed at baseline, discharge, and 6 and 12 months after admission to the hospital. Different aspects of response to treatment including severity of mood and psychotic symptoms, extrapyramidal side effects, global functioning and service satisfaction were assessed using a demographic questionnaire, Young Mania Rating Scale (Y-MRS), and Hamilton Rating Scale for Depression (HAM-D). Results: Severity of symptoms and function showed significant improvement only at discharge (p<0.001), and was not significant afterwards. Patients showed a response rate of 65.4% based on 50% decrease on (Y-MRS), at discharge. Conclusion: Improvement in symptom severity and global functioning was significant at discharge but there was no significant improvement after discharge and during one year follow up.