Plastic surgery patients undergoing either local (LA) or general (CA) anaesthesia of at least fortylive minutes' duration and a non-patient control group were used to examine the extent and duration 0/ deterioration in rnental functioning following CA and the factors influencing such deterioration. Mental jilflctioning was assessed by a ba{(ery of six tests administered one week before anaesthesia, four days after anaesthesia and six weeks after anaesthesia. Mental performance of CA patients but not of LA patients was significantly impaired on the fourth postoperative day. Six weeks ajrer anaesthesia CA patients were still per/orming significantly below controls. There was marked variation in the pallern of recovery, some CA patients failing to regain their pre-operative level 0/ performance after six weeks. Severity of deterioration jollowing general anaesthesia was significantly correlated with habitual ca/leine consllmption.