Of the 1200 non-diabetic offspring of non-insulin-dependent diabetic patients registered under the prevention programme, 262 (M:F 189:73) were available for analysis with greater than or equal to 4 years of follow-up. All of them had been prescribed a calorie restricted diet to suit their body weight, occupation and age, and were advised to restrict the use of refined carbohydrates and fats. Regular exercise was also advised. Compliance with these prescriptions was assessed at each follow up. At the time of analysis, it was noted that only 14.5% had developed diabetes in a period of 8 +/- 4.2 years even though many of them had impaired glucose tolerance at entry in the programme. Multiple regression analysis showed that initial 2 h plasma glucose, initial glucose tolerance and gain in body weight were strong predictors of diabetes. Weight loss occurred in persons who adhered to diet and exercise programmes and conversion to diabetes was lower in them compared to those who gained weight (P < 0.002). Although the rate and degree of obesity is less among Indians, it has been observed in several earlier studies that even a minor increase in body mass index increased the risk of diabetes. This study highlights the fact that measures to control weight helps to delay the onset of diabetes even in the non-obese despite a strong family history of the disorder.