Although most pancreatic islet cell tumors are associated with clinically evident hormone hypersecretion, a small group have no obvious signs or symptoms of excess endocrine activity and are termed "nonfunctioning." The clinical course of eight patients with "nonfunctioning" islet cell carcinoma seen during an eight-year period was reviewed. The six men and two women ranged in age from 36 to 68 years (mean--52). The initial complaint in six was a palpable abdominal mass associated with pain, steatorrhea, or jaundice. Two patients presented with abdominal pain that was initially thought to be of biliary tract origin, and the tumor was discovered at operation. Two patients underwent radical distal pancreatectomy and have no gross evidence of residual or recurrent tumor one and two years later. Five had a biopsy and biliary diversion; three of these also had a gastrojejunostomy. Five were given postoperative 5-fluorouracil and streptozotocin chemotherapy. One developed renal dysfunction and was switched to dimethyltriazenoimidazole carboxamide (DTIC) chemotherapy. Three patients are alive four, six, and eight years, respectively, after diagnosis. Two expired two and a half and three years after diagnosis. One patient had only biopsy of peripancreatic nodes, and he expired in one year. "Nonfunctioning" islet cell carcinoma presents with symptoms related to the mass effects of the tumor. An aggressive therapeutic approach utilizing surgery and chemotherapy is advocated for these slow growing neoplasms.