Two hundred and twenty-two patients with Peutz-Jeghers syndrome were ascertained in Japan between 1961 and 1974 through two nationwide surveys, medical literature, and personal examinations. Genetic analysis was made of this group as well as 102 follow-up cases. The average age at diagnosis was 23 in males and 26 in females, with male to female ratio of 1:1.13. Presenting complaints of 170 patients included obstruction (42.8 per cent of patients), abdominal pain (23.4 per cent), rectal bleeding (13.5 per cent), extrusion of polyp (7.2 percent). Diagnosis of 52 patients was based on melanin pigmentation. Intussusception occurred in 46.9 per cent of the patients, most often in the small intestine. Polyps occurred in the stomach in 108 patients (48.6 per cent), small intestine, 142 patients (64 per cent), colon, 118 patients (53.2 per cent) and rectum, 71 patients (32 per cent). Among the 222 patients, cancer was histologically verified in 28. Fifteen early cancers occurred (3 gastric, 8 small intestine, 4 colon), and 11 advanced cancers (3 gastric, 1 small intestine, 6 colon, and 1 both colon and small intestine). Mortality was lower than in patients with familial polyposis coli but higher than in the general population. Conservative surgical management, planned medical follow-up, and the need for a national registration system are stressed.