BACKGROUND Patients with midgut carcinoid (MGC) tumors are commonly treated with somatostatin analogs. Adverse effects of these drugs include impairment of gallbladder function, formation of gallstones, and cholecystitis. Prophylactic cholecystectomy has been advocated, but data to support this recommendation are sparse. We have analyzed a cohort of 235 patients with MGC focusing on the risk for gallstone formation and complications thereof. METHODS Forty-eight of the 235 patients had been cholecystectomized before surgery for MGC. Of the remaining 187 patients, 144 were treated with somatostatin analogs. Eighteen of the 187 patients had their gall bladder removed during the primary carcinoid surgery. RESULTS Twenty-two of the 144 somatostatin-analog-treated patients developed complications, such as gallbladder empyema (n = 1), cholangitis (n = 2), acute cholecystitis (n = 6), acute pancreatitis (n = 1) or acute pancreatitis and cholecystitis (n = 1), or biliary colic (n = 11). Ninety-two of the 144 were examined during surgery, by computed tomography, or by ultrasound, most for reasons other than gallbladder-related indications, and 63% (58/92) of these examinations revealed gallstones. Of the 43 patients not treated with somatostatin analogs, only 3 patients suffered from biliary colic and underwent cholecystectomy. CONCLUSIONS In our study the incidence of gallstone-related complications seems to be higher than in the general population. We recommend that prophylactic cholecystectomy is liberally performed during laparotomy for MGC if patients are planned to undergo treatment with somatostatin analogs.