OBJECTIVE:To review the causes of nonpancreatic tumor-associated hypoglycemia and report the first case of hypoglycemia attributable to a leiomyosarcoma, which did not cause hypoglycemia in its primary site but only after metastasizing. METHODS:A case report is presented of a 62-year-old man with a gastric leiomyosarcoma diagnosed and surgically treated 8 years previously, who was found to have 14 large, rounded masses in his liver and a blood glucose level of 19 mg/dL. Biopsy of the largest mass revealed a leiomyosarcoma. RESULTS:Evaluation of the cause of the hypoglycemia revealed that circulating insulin, connecting peptide, proinsulin, insulin-like growth factor-I (somatomedin C), and insulin-like growth factor-II levels were below normal, whereas the insulin-like growth factor-II prohormone concentration was increased twofold. Basal and corticotropin-stimulated serum cortisol values were normal. CONCLUSION:This is the first case report of hypoglycemia occurring only after metastasis of a leiomyosarcoma. A possible causal relationship between the hypoglycemia and the increased circulating insulin-like growth factor-II prohormone is suggested, and alternative explanations and treatment are discussed.