Background: The American Diabetes Association (ADA) recommend that fasting glucose alone with the oral glucose tolerance test should be used to diagnose diabetes mellitus. We assessed mortality associated with the ADA fasting-glucose criteria compared with the WHO 2 h post-challenge glucose criteria. Methods: We assessed baseline data on glucose concentrations at fasting and 2 h after the 75 g oral glucose tolerance test from 13 prospective European cohort studies, which included 18,048 men and 7316 women aged 30 years or older. Mean follow-up was 7.3 years. We assessed the risk of death according to the different diagnostic glucose categories. Findings: Compared with men who had normal fasting glucose (< 6.1 mmol/L), men with newly diagnosed diabetes mellitus by the ADA fasting criteria (≥ 7.0 mmol/L) had a hazard ratio for death of 1.81 (95% CI 1.49-2.20); for women the hazard ratio was 1.79 (1.18-2.69). For impaired fasting glucose (6.1-6.9 mmol/L), the hazard ratios were 1.21 (1.05-1.41) and 1.08 (0.70-1.66). For the WHO criteria (≥ 11.1 mmol/L), the ratios for newly diagnosed diabetes were 2.02 (1.66-2.46) in men and 2.77 (1.96-3.92) in women, and for impaired glucose tolerance (7.8-11.1 mmol/L) were 1.51 (1.32-1.72) and 1.60 (1.22-2.10). Within each fasting-glucose classification, mortality increased with increasing 2 h glucose. However, for 2 h glucose classifications of impaired glucose tolerance, and diabetes, there was no trend for increasing fasting glucose concentrations. Interpretation: Fasting-glucose concentrations alone do not identify individuals at increased risk of death associated with hyperglycaemia. The oral glucose tolerance test provides additional prognostic information and enables detection of individuals with impaired glucose tolerance, who have the greatest attributable risk of death.