Octreotide exerts a wide range of biological actions, many of which have important clinical applications, notably in treatment of acromegaly, gastroenteropancreatic endocrine tumors, and secretory diarrhea. In most patients, octreotide is well tolerated. Side effects are primarily gastrointestinal and are usually transient. Short term (< or = 1 month) octreotide therapy appears to pose minimal risk of gallstone formation, but the risk may increase with longer treatment periods. Chronic octreotide administration may increase the incidence of small, cholesterol gallstones that are typically asymptomatic. The mechanism of octreotide-associated gallstone formation is not delineated but may involve inhibition of gallbladder emptying, hepatic bile secretion, and sphincter of Oddi motility, as well as modification of bile composition. Gallbladder stasis may sequentially lead to increased bile concentration, precipitation of cholesterol and calcium salts, retention of biliary precipitates, and maturation of gallstones. Octreotide-associated gallstones are usually asymptomatic and do not require surgical or medical therapy. Some physicians advocate periodic gallbladder ultrasound evaluations, but, in most cases, the results would not influence management of asymptomatic patients. Symptomatic gallstones may require surgery or nonsurgical treatments after an appropriate work-up. Gallstone prevention strategies (e.g., bile acid or nonsteroidal anti-inflammatory drug therapy) during long term octreotide therapy are under investigation. Currently, clinicians may want to consider noninvasive strategies to reduce gallstone incidence, such as timing octreotide injections in relation to meals or periodic cessation of octreotide treatment. Octreotide is a valuable therapeutic option in managing a variety of hypersecretory states associated with high morbidity and mortality (e.g., acromegaly, carcinoid syndrome, and VIP-secreting tumors), so the benefits of long term octreotide therapy (such as increased quality of life) outweigh the risk of asymptomatic gallstone formation in many patients.