Sleep disturbance is a common feature during mood episodes in bipolar disorder. The aim of this study was to investigate the prevalence of such symptoms among euthymic bipolar patients, and their association with risk for mood episode recurrence. A cohort of bipolar I and II subjects participating in the Systematic Treatment Enhancement Program for Bipolar Disorder who were euthymic for at least 8 weeks were included in this analysis. Survival analysis was used to examine the association between sleep disturbance on the Montgomery-Asberg Depression Rating Scale (MADRS) and recurrence risk. A total of 73/483 bipolar I and II subjects reported at least mild sleep disturbance (MADRS sleep item ≥2) for the week prior to study entry. The presence of sleep problems was associated with a history of psychosis, number of previous suicide attempts, and anticonvulsant use. Sleep disturbance at study entry was significantly associated with risk for mood episode recurrence. Sleep disturbance is not uncommon between episodes for individuals with bipolar disorder and may be associated with a more severe course of illness. This suggests that sleep disturbance is an important prodromal symptom of bipolar disorder and should be considered a target for pharmacologic or psychosocial maintenance treatment.