"Double diabetes," which refers to the coexistence of type 1 and type 2 diabetes mellitus, is a newly coined term in the diabetic literature. Excessive weight gain and a family history of type 2 diabetes in a patient with type 1 diabetes are the possible major causes. We report a case of double diabetes in a 45-year-old patient with type 1 diabetes mellitus that developed after insulin pump therapy. Insulin pump therapy is a valuable method used in the management of type 1 diabetes mellitus that may provide life comfort. However, this comfort may result in excessive weight gain, which, when combined with a family history of type 2 diabetes mellitus, may predispose to double diabetes. Clinicians must consider this pattern during the use of insulin pump therapy in patients with type 1 diabetes.