Effective, long-term therapy for bipolar disorders is a critical goal of mental health care, but achieving this goal is complicated by numerous factors in real clinical settings. The aim of this study was to investigate dropout patterns and their associated factors in patients with bipolar disorders.The study participants were 275 patients with DSM-IV bipolar disorders, receiving planned maintenance treatment among patients at the Mood Disorders Clinic of Seoul National University Bundang Hospital between January 2005 and December 2007. The rates of dropout in patients were prospectively examined for 3 years. The factors affecting the dropouts were analyzed using a Cox regression model.The dropout rates were 10.9%, 20.4%, 24.7%, 33.8%, 44.0%, and 50.2% at 1, 3, 6, 12, 24, and 36 months after treatment entry, respectively. The dropout rates increased rapidly during the first three months and slowed after 12 months. Past psychotic symptoms (HR 0.523, 95% CI 0.339-0.807), longer illness duration (HR 0.975, 95% CI 0.955-0.966), past psychiatric diagnoses (bipolar disorder, HR 0.242, 95% CI 0.120-0.490; other axis I disorders 0.434, 95% CI 0.268-0.701), and a past history of dropouts (HR 1.746, 95% CI 1.028-2.965) significantly influenced the time to dropout in bipolar patients. The main reasons for dropout were 'denial of therapeutic need' (34.8%) and 'lack of treatment efficacy' (23.2%). Dropout from the maintenance phase of treatment was mainly attributed to the patients' poor understanding of the effects of their treatment.A high early dropout rate for subjects with bipolar disorders was observed in this study, suggesting an increased risk for insufficient maintenance treatment. These results may support the role of psychoeducational approaches in enhancing adherence to treatment, as well as social approaches to improving public awareness. Following the early evaluation of a patient's concept of bipolar disorders, individualized psychoeducational strategies are necessary to improve the long-term outcomes for subjects with bipolar disorders.