Five adult Samoyed dogs from two unrelated litters were diagnosed with diabetes mellitus. Two full-sibling male dogs (Family A) were raised in the same household. The other three dogs, two female and one male, were also full siblings (Family B) raised in different households. All five dogs developed polyuria and polydipsia and demonstrated fasting hyperglycemia and glucosuria. Diabetes mellitus was diagnosed in all five dogs and responded to appropriate therapy with insulin. The occurrence of insulin-dependent diabetes mellitus in multiple, closely related Samoyed dogs suggests a familial predisposition in this breed.