A population-based survey in 1996 and 1997 of 770 adults (aged > or = 15 years) from an urban district of Dares Salaam and 928 from a village in rural Kilimanjaro district (Tanzania) revealed that the prevalence of diabetes, impaired fasting glucose (IFG), overweight, obesity, and physical inactivity was higher in the urban area for men and women. The difference between urban and rural prevalence of diabetes was 3.8 [1x1-6.5]% for men and 2x9 [0x8-4.9]% for women. For IFG, the difference was 2x8 [0x3-5x3]% for men and 3x9 [1x4-6x4]% for women; for overweight and obesity, the difference was 21.5 [15.8-27.1]% and 6.2 [3x5-8.9]% for men and 17x4 [11.5-23.3]% and 12.7 [8x5-16x8]% for women, respectively. The difference in prevalence of physical inactivity was 12x5 [7.0-18.3]% for men and 37.6 [31x9-43.3]% for women. For men with diabetes, the odds for being overweight, obese and having a large waist:hip ratio were 14.1, 5.3 and 12.5, respectively; for women the corresponding values were 9x0, 10x5 and 2x4 (the last not significant) with an attributable fraction for overweight between 64% and 69%. We conclude that diabetes prevalence is higher in the urban Tanzanian community and that this can be explained by differences in the prevalence of overweight. The avoidance of obesity in the adult population is likely to prevent increases in diabetes incidence in this population.