We are reporting here the extent of weight change over 6.5 years of follow-up amongst 366 randomly selected Nauruans initially surveyed in 1975-1976. Although the initial level of obesity was high (mean body mass index: males 30.8 kg/m2, females 33.0 kg/m2), further increase in body mass index subsequently occurred in 285 subjects (78%). The weight loss that occurred amongst the other 81 subjects was generally mild (mean = 5.3 kg), and only 12 persons lost more than 10 kg. Weight loss was far more common amongst the older subjects: 40% of those older than 50 years compared with 10% of those less than 30 years showed a decrease in body mass index (P less than 0.001). After age adjustment, greater initial obesity was associated with subsequent weight loss (P less than 0.001), and higher baseline plasma glucose (P less than 0.001), and triglyceride levels (P less than 0.05) and lower plasma uric acid levels (P less than 0.01) were also predictive of some weight loss. Obesity and diabetes remained the major predictors of weight loss in the multivariate analysis. Subjects who lost weight showed similar deterioration in glucose tolerance over the 6.5 years (mean increase = 1.8 mmol/l) to those not losing weight (mean = 1.0 mmol/l) and weight loss was not associated with glucose tolerance improvement (or less deterioration) for either those diabetic, or those not diabetic initially. This result suggests that weight loss is not invariably associated with improvement in glucose tolerance amongst Nauruans.