During examination before surgical correction of pes valgus a 20-year-old man reported having 3-5 pasty, foul smelling diarrhoeic motions per day for the past 3 years. He was noted to have rather thick lips and Marfan-like body build. Erythrocyte sedimentation rate was 18/34 mm, serum activity of GOT 22.5 U/l, GPT 35.7 U/l. Faecal weight was increased to 640 g/d, fat content to 12 g/d. Serum levels of the carcinoembryonic antigen (2494 ng/ml; normal: < 2.5) and of calcitonin (1,619,760 pg/ml; normal < 100) were elevated. Gastroscopy, partial coloscopy, colon-contrast imaging, ultrasonography and computed tomography of the neck and abdomen, as well as magnetic nuclear imaging of the neck were all normal. But laparoscopy revealed the liver to be infiltrated by small whitish nodules which immunohistologically proved to be metastases of a C-cell carcinoma. Total thyroidectomy was performed and the diagnosis of a C-cell carcinoma of the thyroid confirmed intra-operatively. After the operation the diarrhoea was stopped with codeine (9 mg/d). In case of tumour progression, therapy with octreotide, a somatostatin analogue, will be carried out. The concomitant occurrence of C-cell carcinoma, Marfan-like body build, thick lips and skeletal changes is typical of multiple endocrine neoplasia type 2B, which is caused by a chromosomal defect.