Hypoglycemia associated with nonislet cell tumor was found in 13 dogs. In each dog, clinical signs were related directly to adrenergic and neuroglucopenic effects of hypoglycemia and included collapsing episodes, tremors, restlessness, weakness, and grand mal seizures that were responsive to glucose administration. Eight of the dogs had hepatocellular carcinoma; surgical resection of the tumor achieved remission of clinical signs in 3 of these dogs. Other hepatic tumors associated with hypoglycemia included leiomyosarcoma and hemangiosarcoma involving solitary lobes of the liver. Nonhepatic tumors included splenic hemangiosarcoma, diffuse metastatic melanoma, and salivary gland adenocarcinoma.