Previous studies on type 2 diabetes mellitus in the Islamic Republic of Iran were mainly performed in provinces with large populations. This study determined the prevalence and risk factors of diabetes mellitus in an adult population (40–80 years old) from Yazd district. Multistage, systematic cluster random sampling was used in a cross-sectional, population-based survey. Demographic, clinical and anthropometric data were collected, with diabetes defined as fasting blood sugar ≥ 7 mmol/L or a positive medical history of diabetes. The age- and sex-standardized prevalence of diabetes in 2090 individuals participants was 24.5% (95% CI 22.2–26.8%), including 10.5% new cases. For each year of ageing, the prevalence of diabetes increased significantly by 4% and this trend was more pronounced in females than males. Low education and hypertension were significantly associated with diabetes prevalence. The prevalence of diabetes mellitus in Yazd is greater than the average levels nationwide and those of nearby countries.