New-onset diabetes mellitus (NODAT) is a serious complication following renal transplantation. In this cohort study, we studied 118 nondiabetic renal transplant recipients to examine whether indices of insulin resistance and secretion calculated before transplantation and at 3 months post-transplantation are associated with the development of NODAT within 1 year. We also analysed the long-term impact of early diagnosed NODAT. Insulin indices were calculated using homeostasis model assessment (HOMA) and McAuley's Index. NODAT was diagnosed using fasting plasma glucose. Median follow-up was 11 years. The cumulative incidence of NODAT at 1 year was 37%. By logistic regression, recipient age (per year) was the only significant pretransplant predictor of NODAT (OR 1.04, CI 1.009–1.072), while age (OR 1.04, CI 1.005–1.084) and impaired fasting glucose (OR 2.97, CI 1.009–8.733) were significant predictors at 3 months. Pretransplant and 3-month insulin resistance and secretion indices did not predict NODAT. All-cause mortality was significantly higher in recipients developing NODAT within 1 year compared with those remaining nondiabetic (44% vs. 22%, log-rank P = 0.008). By Cox's regression analysis, age (HR 1.075, CI 1.042–1.110), 1-year creatinine (HR 1.007, CI 1.004–1.010) and NODAT within 3 months (HR 2.4, CI 1.2–4.9) were independent predictors of death. In conclusion, NODAT developing early after renal transplantation was associated with poor long-term patient survival. Insulin indices calculated pretransplantation using HOMA and McAuley's Index did not predict NODAT.