Heart failure (HF) and type 2 diabetes mellitus (T2DM) exhibit a well-established interrelationship and a growing prevalence, in particular in elderly people. Cardiac resynchronization therapy (CRT) has been shown to improve myocardial function in patients with HF and cardiac dyssynchrony. However, reports on CRT in diabetic elderly patients are limited and controversial. Therefore, the aim of the present study was to investigate the functional role of T2DM on the effectiveness of CRT at advanced age. In this single-center prospective study, we enrolled 72 HF patients over 75 years old with and without T2DM who underwent CRT implant. Detailed clinical and instrumental data, including cardiac ultrasound analysis, 6-min walk test, and quality-of-life evaluation, were collected at baseline and at 1-year follow-up. At the time of implantation, 44.4 % of patients had T2DM, of which 62.5 % were well controlled with diet and hypoglycemic drugs and 37.5 % were treated by insulin therapy. After 1 year, CRT improved myocardial ventricular geometry and functional capacity in a comparable proportion of diabetic and non-diabetic patients alongside with a similar amelioration in the functional status. Taken together, our findings demonstrate that diabetic patients >75 years old exhibit a response to CRT that is comparable to non-diabetic subjects.