BACKGROUND: The aim of the present study was to determine the prevalence and risk factors of prediabetes and diagnosed and undiagnosed diabetes mellitus (DM) in rural Bangladesh. METHODS: Using a population-based cluster random sampling strategy, 3104 adults aged ≥30 years were recruited. Fasting capillary blood glucose, blood pressure, height, weight, waist circumference, and knowledge, attitudes, and practice related to diabetes were recorded. Diabetes was defined as fasting glucose (FG) ≥7.0 mmol/L or a self-reported diagnosis of diabetes; impaired FG (IFG) was defined as FG ≥ 6.1 and <7.0 mmol/L. RESULTS: The overall crude prevalence of DM was 7.2% (95% confidence interval [CI] 6.3%-8.1%; n = 222), of which 55% (n = 123) was previously undiagnosed (UDM). The prevalence of IFG was 5.3% (95% CI 4.5%-6.1%; n = 163). The age-standardized prevalence of DM and IFG was 6.6% and 5.0%, respectively. The prevalence of UDM was higher in people of lower socioeconomic status (59% vs 31%; P < 0.001). Of those with known DM, 56% had poor glycemic control (FG ≥ 7.0 mmol/L) and 37% were not on medication. Overall knowledge of DM was poor; only 16.3%, 17.8%, and 13.4% of those with UDM, IFG, and normal FG knew that diabetes causes eye disease, compared with 55.6% of those with known DM (Ptrend  < 0.001). CONCLUSIONS: In this rural Bangladeshi community, UDM was high. Lower socioeconomic status was associated with a higher risk of UDM. Overall knowledge of DM was poor. Public health programmes should target those of low socioeconomic status and aim to increase knowledge of DM in rural Bangladesh. © 2015 Ruijin Hospital, Shanghai Jiaotong University School of Medicine and Wiley Publishing Asia Pty Ltd.