We performed screening polysomnography on 86 inpatients with affective disorders and found that 13 (15.1 per cent) had sleep apnea and one had nocturnal myoclonus. The apnea tended to be extremely mild, with an average of 27.8 episodes per patient and with a mean duration of 15.0 seconds. No clinically significant cardiac arrhythmia accompanied the apnea. The apnea was predominantly obstructive or mixed, not central. Only four patients (4.7 per cent) had apnea indices greater than five, and even here the total apnea was considered mild. Much of the apnea (68.3 per cent) occurred during rapid eye movement sleep. While there was no association of apnea with gender or with type of sleep-wake complaint, a significant relationship with age emerged. On the basis of these data, we suggest that routine polysomnographic screening for sleep apnea and nocturnal myoclonus in affective disorders is not indicated. On occasion, however, both an affective disorder and a sleep-apnea syndrome co-exist in the same patient. In such cases, the sleep-wake complaint is usually very prominent and/or long-standing in relation to other psychopathology and requires appropriate polysomnographic evaluation.