OBJECTIVE To compare outcome of surgical versus medical treatment of dogs with beta cell neoplasia. DESIGN Retrospective study. ANIMALS 39 dogs with clinical signs of hypoglycemia and serum glucose and insulin concentrations consistent with a diagnosis of beta cell neoplasia. PROCEDURE Information on signalment; clinical history; physical examination findings; results of CBC, serum biochemical analyses, and urinalysis; serum glucose and insulin concentrations; results of thoracic radiography and abdominal ultrasonography; treatment and treatment complications; survival time; and cause of death were obtained from medical records. RESULTS 26 dogs underwent exploratory celiotomy and partial pancreatectomy; 13 dogs were treated medically (i.e., dietary change and prednisone). Median survival time was significantly longer for dogs treated surgically than for dogs treated medically. Significant differences were not found in mean age, body weight, duration of clinical signs prior to diagnosis, serum glucose and insulin concentration, or results of other serum biochemical tests between dogs treated surgically and dogs treated medically; also, there was no significant correlation between any of these parameters and survival time for either group of dogs. CONCLUSIONS AND CLINICAL RELEVANCE Results suggest that exploratory celiotomy and partial pancreatectomy are indicated once a tentative diagnosis of beta cell neoplasia is established in dogs.