Results: The evidence cited within this paper suggests that sleep disturbances frequently precede bipolar disorder by several years and convey an elevated long-term risk for developing any kind of mood disorder. Disordered sleep appears to emerge about the time of puberty and remains persistently elevated in individuals at high risk. Conclusion: Disturbed sleep appears to be an early symptom of bipolar disorder but further research, especially longitudinal studies in individuals at high risk, will be required to characterize the type and patterns more precisely.