['Cardiac resynchronization therapy (CRT) improves cardiac performance and survival in patients with congestive heart failure. Recent observations suggest that diabetes is associated with a worse outcome in these patients. The aim of the study was to investigate the effect of diabetes and insulin treatment on outcome after CRT.', 'Diabetic status and insulin treatment were assessed in 447 patients who underwent CRT (males 80.8%, mean age 65.7 +/- 9.7 years, ejection fraction 29.9 +/- 6.11%). Patients were stratified in three groups according to the presence or absence of diabetes and insulin treatment.', 'Nondiabetic patients were 366 (79.6%), noninsulin-treated diabetic patients 62 (13.9%), insulin-treated diabetic patients 29 (6.5%). The estimated death rate was 5.15 per 100 patients-year in the nondiabetic group, 8.63 in noninsulin-treated diabetics (HR 1.59, P = 0.240), and 15.84 in insulin-treated diabetics (HR 3.05, P = 0.004). Cardiac mortality accounted for 81% of deaths in nondiabetic patients and for 56% of deaths in diabetic patients. Diabetic patients tended to have a worse recovery of left ventricular ejection fraction over time (P = 0.057) and of the distance at 6-minute walking test (6MWT) (P = 0.018).'] Is insulin-treated type 2 diabetes associated with a decreased survival in heart failure patients after cardiac resynchronization therapy?