The authors report a case of Peutz-Jeghers syndrome in a young patient revealed by a duodenal carcinoma developed in a hamartomatous polyp. The absence of adenomatous lesion a the level of duodenal tumour, and the presence of hamartomatous lesions, particularly smooth muscular fibres, contiguous to carcinomatous glands, are favorable to a degenerescence of hamartomatous polyp. The question of malignant change or of the association of digestive carcinomas is discussed.