Tokelauans show an increased prevalence and incidence of diabetes mellitus after migration to the modern industrial society of New Zealand (NZ). In females the prevalence rose from 6.1 percent before migration to 10.8 percent afterwards, while in males a nonsignificant rise from 2.3 percent to 4.4 percent was observed. Migrants who had been in New Zealand for longer periods had higher incidence than other migrants. Time since arrival in New Zealand was a significant predictor of diabetes, but time spent in an intermediate environment, Samona, on the way to New Zealand was not. Increase in body weight and adiposity occurred in the migrants. Adiposity was associated with an increased risk of diabetes, but nonspecific weight increase was not. Diabetic females had experienced 15 percent more births than nondiabetic females. Changed energy balance related to diet and work patterns may be related to the increased incidence of diabetes in migrants, in a population predisposed by high serum uric acid concentrations, obesity and high fertility.