The prevalence of type 2 diabetes and impaired glucose tolerance (IGT) is increasing in urban areas of developing countries, especially in India. This is a report of the temporal changes in the prevalence of diabetes and IGT in urban areas of Chennai (Madras), India, in adults aged > or =20 years, with an emphasis on identifying the risk factors responsible for the changes. Three urban diabetic surveys conducted in 1989, 1995 and 2000 were compared for the age-standardized prevalence, anthropometric, demographic and lifestyle characteristics of the glucose-intolerant groups. Multiple logistic regression analyses were used for the identification of risk variables associated with diabetes and IGT. The trend was statistically significant for diabetes (chi(2)=18.0, P<0.001) and for IGT (chi(2)=48.2, P<0.001). The period between 1989 and 1995 showed a 40% rise in the prevalence of diabetes and a further increase of 16.4% in the next 5 years. Age increased in each survey for both genders. Waist girth and waist:hip ratio were significantly higher in women, in the 2000 survey. There was no change in the mean body mass index with time in both genders. An increase in IGT was seen in year 2000, especially so in subjects aged <40 years. The prevalence of diabetes and IGT is increasing in India. Increasing age and positive family history showed associations with diabetes.