The prevalence of diabetes mellitus and impaired glucose tolerance (IGT) and their relationship to age and obesity was estimated in the rural town of Shikarpur in Sindh Province, Pakistan by a population-based survey in 1994. Oral glucose tolerance tests were performed in a stratified random sample of 967 adults (387 men, 580 women) aged 25 years and above. The diagnoses of diabetes and IGT were made on the basis of WHO criteria. The response rate was 71% for men and 80% for women. The prevalence of diabetes was 16.2% (9.0% known, 7.2% newly diagnosed) in men, and 11.7% (6.3% known, 5.3% newly diagnosed) in women. The prevalence rose with age to a peak of 30% and 21% in 65-74 year-old men and women respectively. IGT was detected in 8.2% of men and 14.3% of women. Thus, total glucose intolerance (diabetes and IGT combined) was present in 25% of subjects examined. These results indicate that glucose intolerance in South Asians can no longer be regarded as a problem confined to migrant communities. Of the 72 subjects previously known to have diabetes, none was using insulin treatment, but 57 (79%) took oral hypoglycaemic agents. Central obesity and positive family history were strongly associated with diabetes, as was prevalence of hypertension. The association with central obesity was greater for women than for men, and suggests important, modifiable risk factor(s) related to lifestyle.