The psychiatric morbidity associated with mastectomy was assessed in 75 women by following them up from the time they presented with suspected breast cancer to one year after the operation. Fifty women with benign breast disease served as controls. Throughout the follow-up period the incidence of psychiatric problems was higher among the women who had undergone mastectomy. One year after surgery 19 (25%) of these women compared with only 5 (10%) of the controls needed treatment for anxiety or depression or both, and 16 (33%) compared with 3 (8%) respectively had moderate or severe sexual difficulties. Altogether 29 patients in the mastectomy group (39%) and six of the controls (12%) had serious anxiety, depression, or sexual difficulties. Of the eight women in the mastectomy group who sought help for their problems, only two felt that the help given had been appropriate. The inability to recognise and treat these emotional disturbances is a common and serious problem. Monitoring by specially trained nurses and social workers might help to identify them earlier and even reduce them.