OBJECTIVES: To study the characteristics of UK individuals identified with non-diabetic hyperglycaemia (NDH) and their conversion rates to type 2 diabetes mellitus (T2DM) from 2000 to 2015, using the Clinical Practice Research Datalink. DESIGN: Cohort study. SETTINGS: UK primary Care Practices. PARTICIPANTS: Electronic health records identified 14 272 participants with NDH, from 2000 to 2015. PRIMARY AND SECONDARY OUTCOME MEASURES: Baseline characteristics and conversion trends from NDH to T2DM were explored. Cox proportional hazards models evaluated predictors of conversion. RESULTS: Crude conversion was 4% within 6 months of NDH diagnosis, 7% annually, 13% within 2 years, 17% within 3 years and 23% within 5 years. However, 1-year conversion fell from 8% in 2000 to 4% in 2014. Individuals aged 45-54 were at the highest risk of developing T2DM (HR 1.20, 95% CI 1.15 to 1.25- compared with those aged 18-44), and the risk reduced with older age. A body mass index (BMI) above 30 kg/m2 was strongly associated with conversion (HR 2.02, 95% CI 1.92 to 2.13-compared with those with a normal BMI). Depression (HR 1.10, 95% CI 1.07 to 1.13), smoking (HR 1.07, 95% CI 1.03 to 1.11-compared with non-smokers) or residing in the most deprived areas (HR 1.17, 95% CI 1.11 to 1.24-compared with residents of the most affluent areas) was modestly associated with conversion. CONCLUSION: Although the rate of conversion from NDH to T2DM fell between 2010 and 2015, this is likely due to changes over time in the cut-off points for defining NDH, and more people of lower diabetes risk being diagnosed with NDH over time. People aged 45-54, smokers, depressed, with high BMI and more deprived are at increased risk of conversion to T2DM.