In a 26-year-old woman with symptoms of hyperinsulinism explorative laparotomy revealed a pancreatic tumour metastatizing into the liver. Intensive cytostatic therapy led to a temporary inhibition of hyperinsulinism, however, in the course of two years massive infiltration of the retroperitoneum, left adrenal, gastric wall, liver, mesentery and abdominal lymph nodes by a tumour occurred. On necroptic examination the tumour had characteristics of a neuroendocrine carcinoma with carcinoid features. Part of the tumour cells were argyrophil; reliable evidence of insulin production, which during the terminal stage of the disease played again a major part in the clinical picture, was made possible only by the use of a very sensitive Czech made antibody against C peptide.