Endocrine pancreatic tumors are slowly growing neuroendocrine neoplasms with a malignant potential which may cause symptoms such as hypoglycemia, multiple ulcers, diarrhea, flush, hyperglycemia and skin rash. A prospective study was performed on 84 patients with endocrine pancreatic tumors. In 59 patients (70%) the tumors were malignant. Of the 84 patients, 23 had insulinomas, 25 gastrinomas, 20 nonfunctioning tumors, 14 the WDHA syndrome, 1 somatostatinoma and 1 glucagonoma. The median age at diagnosis was 53 years and the median delay from first symptom to diagnosis was 2 years. The most common site of the pancreatic primary tumor was the tail (41%), and metastases were most frequently located in the liver (60%) and lymph nodes (44%). Plasma chromogranin A + B was elevated in 94%, serum pancreatic polypeptide (PP) in 74%, plasma neurotensin in 67% and serum gastrin in 62%. Serum HCG-alpha and -beta subunits were elevated in 41 and 30% respectively, all except 3 having a verified malignant tumor. The median survival from first symptom and diagnosis was 14.2 and 8.7 years respectively. Patients with MEN-1 had a significantly better survival from diagnosis than sporadic cases (median 15.1 versus 5.8 years). Patients who received interferon after failing chemotherapy had a significantly better survival than those given chemotherapy alone (5-year survival 65 and 50% respectively).