Eighty-five patients with endocrine pancreatic tumors associated with clinical syndromes of hormone excess were retrospectively analyzed regarding symptomatology, means of diagnosis, and results of surgical and medical treatment during follow-up of 3-18 years (median 8 years). The combination of angiography and computed tomography was most successful in pre-operative localization of both primary tumors and metastases. Surgery provided long term cure in 39 of 44 patients with benign islet cell lesions, the majority having insulinomas. Forty-one patients had malignant tumors, which at the time of diagnosis or operation were associated with liver and/or regional lymph gland metastases in 56% and 24%, respectively. Sixteen patients with metastatic disease and/or very large tumors were considered inoperable, 5 patients underwent palliative resection of their malignant tumors, while grossly radical tumor removal was accomplished in 20 patients. Long-term cure was achieved in 5 patients by excision of primary tumors and localized liver or lymph gland metastases. Half of the patients, particularly those with insulinoma, gastrinoma, or vipoma, showed response to streptozotocin, in combination with other cytostatics, for a median of 24 months or a response to interferon for a median of 10 months. The overall 5-year and 10-year survival among the patients with malignant islet cells tumors was 54% and 28%, respectively. Absence of liver metastases at time of operation/diagnosis, smaller size of the primary tumor, grossly radical tumor resection as well as response to medical therapy predicted the more favorable survival.