Seventy-four survivors of acute carbon monoxide poisoning were followed up for an average of three years. In eight patients gross neuropsychiatric damage was directly attributable to the poisoning. Three patients had committed suicide and eight had died from other causes. Morbidity and mortality in those deliberately and accidentally poisoned was approximately equal.Of 63 patients alive at follow-up eight showed an improvement and 21 (33.3%) a deterioration of personality after poisoning, and 27 (43%) reported a subsequent impairment of memory. Deterioration of personality and memory impairment were highly correlated. The level of consciousness on admission to hospital in the acute phase of poisoning correlated significantly with the development of gross neuropsychiatric sequelae. These findings emphasize the importance of prompt and efficient treatment of carbon monoxide poisoning and the need to follow-up all cases in the anticipation of a relapsing course or the development of sequelae.