Puerperal psychosis is a rare but serious psychiatric disorder following delivery. Although controversy continues to surround its nosological status, puerperal psychosis is generally considered a mood episode with psychotic features occurring in the context of bipolar disorder or schizoaffective disorder. Due to the close temporal association with childbirth, the etiological role of gonadal steroids, particularly estrogen, has been considered. Familial factors have also been implicated in the triggering of episodes of puerperal psychosis. Sleep deprivation arising from an array of diverse factors is a common occurrence surrounding parturition. The author suggests that sleep loss plays a pivotal role in the causation of puerperal psychosis. Clinical implications of this hypothesis are discussed. Studies on the aetiology and pathogenesis of puerperal psychosis are urgently needed not only for prevention and better treatment strategies of puerperal psychosis but also for understanding the biological underpinnings of bipolar disorder.