To evaluate the psychological disturbances associated with obstructive sleep apnea (OSA) and the effect of nasal continuous positive airway pressure (NCPAP) treatment on these alterations, personality patterns and psychosocial adjustment were assessed in patients hypnopolygraphically diagnosed with OSA before and after different periods of NCPAP therapy. Prior to treatment, MMPI results for 23 patients showed significant elevations (p < .01) on five clinical scales compared to those of 17 normal controls. Apneics' personality patterns were predominantly of a "neurotic-mixed" type, indicating an anxiety reaction with paranoid features. Depression, schizophrenia, and hypochondriasis were the highest scales. Most patients had severe psychosocial maladjustment. In the follow-up study during the NCPAP treatment, there was a progressive reduction of the psychopathological signs along with a generalized improvement in psychosocial adaptation. These changes were remarkably significant after about a year's treatment, in particular for depression (p < .01) and total adjustment degree (p < .01). It was concluded that severe OSA is associated with serious psychosocial alterations that improve gradually with NCPAP.