Seventy-four myasthenic patients (54 F, 20 M; mean age 49.6 years) were evaluated using the diagnostic criteria of the DSM-III in order to investigate the prevalence of psychiatric disturbances in this order. Fifty-one had had thymectomies, of whom 28 females had hyperplasia, two females and five males had involution of the thymus, and 10 females and six males had thymomata. Psychiatric disturbances were observed in 38 subjects (51%), in particular, adjustment disorders with depressed mood and mixed emotional features (19%) (22% including adjustment disorder with anxious mood), affective disorders (13.5%) and personality disorders (18%).