A case of metastasising colonic carcinoma associated with Peutz-Jeghers syndrome in a 39 year old man is described. The caecal adenocarcinoma had metastasised widely to regional lymph nodes and was associated with several other colonic Peutz-Jeghers polyps, showing no evidence of dysplasia or malignancy. It was not possible to determine whether the carcinoma had arisen from a Peutz-Jeghers polyp. The patient also had gastric and small intestinal polyps. The serum carcinoembryonic antigen (CEA) was normal at presentation in this patient and in one other reported case. The use of this determination as a screening test for so-called high risk groups is, therefore, not supported by this report. The risk of malignancy is not known. It will only be determined by careful follow up of a defined Peutz-Jeghers syndrome population and comparison of carcinoma incidence with a matched sample of the general population. A national registry of Peutz-Jeghers syndrome patients in the United Kingdom would help to resolve this question.