A survey of pituitary diseases in Japan during the 10 yr period between 1965 and 1974 is reported. It was estimated that total number of patients was 1130 cases of pituitary dwarfism, 1908 cases of hypopituitarism, 917 cases of acromegaly and gigantism, 745 cases of Cushing''s disease (adrenal hyperplasia) and 1668 cases of pituitary diabetes insipidus. Detailed information was obtained on about half of these patients. Among patients with pituitary dwarfism, 84% were idiopathic. Idiopathic cases were observed far more frequently in male patients, while no sexual dominancy was observed in secondary cases. In adult males with hypopituitarism, 42% were due to pituitary adenomas, 19% to craniopharyngiomas and 14% to pinealomas; in adult females, 42% were due to Sheehan''s disease, 30% to pituitary adenomas, 12% to cranipharyngiomas and only 3% to pinealomas. In patients with acromegaly, male to female ratio was 1.2:1; histologically, 72% were acidophilic, 13% chromophobe and 15% mixed pituitary adenomas. In this survey of Cushing''s disease, Cushing''s syndrome, due to adrenal tumor was 2:1. Male to female ratio was 1:3.3 in hyperplasia and 1:3.9 in adrenal tumor. In patients with pituitary diabetes insipidus, 55% were secondary, 45% idiopathic and 2% familial. Sex ratio between males and females was 1.4:1. As causes of secondary cases, 25% were due to pinealomas, 16% craniopharygiomas, 13% trauma and 11% other brain tumors.