BACKGROUND. Body fat accumulation decreases insulin sensitivity. It has being associated with earlier onset of type 1 diabetes mellitus (DM) and islet graft failure. The aim of this study was to evaluate whether insulin resistance, characterized by risk factors for type 2 DM, can predict islet graft survival in type 1 DM islet transplant (ITx) recipients. METHODS. Demographic, anthropometrical, and laboratory data, as well as family history of type 2 DM (first degree relatives), were collected from 44 ITx recipients. Risk factors for type 2 DM, such as positive family history of type 2 DM (n=11) and overweight (body mass index >25 kg/m; n=14), were analyzed separately and in combination, which was designated as "type 2 DM phenotype" (n=5). Differences in outcomes (time-to-graft dysfunction and failure) were compared using Kaplan-Meier curves. Cox regression analysis was performed to control for possible confounding factors. RESULTS. Neither positive family history of type 2 DM nor overweight at baseline could predict islet function outcomes after ITx. However, when both risk factors were grouped, the "type 2 DM phenotype" was associated with earlier islet graft failure (mean estimate graft survival 25.7±9.1 vs. 54.1±5.2 months, P=0.022). These results were sustained after adjustments for confounding variables (OR 5.20, 95% CI 1.12-24.0). CONCLUSIONS. Predisposition for type 2 DM can coexist with the type 1 DM phenotype and is associated with earlier decline in islet graft function. Prospective clinical trials should address whether it is associated with decreased insulin sensitivity and if insulin sensitizers play a role in prolonging islet graft survival. © 2009 Lippincott Williams & Wilkins, Inc.