Low concentrations of plasma adiponectin, the most abundant adipose-specific protein, are observed in obese individuals and predict the development of type 2 diabetes. Administration of adiponectin to rodents prevented diet-induced weight gain, suggesting a potential etiologic role of hypoadiponectinemia in the development of obesity. Our aim was to prospectively examine whether low plasma adiponectin concentrations predict future weight gain in Pima Indians, explaining the predictive effect of adiponectin on the development of type 2 diabetes. We measured plasma adiponectin concentrations in 219 nondiabetic Pima Indians (112 M/107 F, age 31 +/- 9 years, body weight 96 +/- 20 kg [mean +/- SD]) in whom body weight and height were measured and BMI calculated at baseline and follow-up. Cross-sectionally, plasma adiponectin concentrations were negatively associated with body weight (r = -0.28, P = 0.0001). Prospectively, plasma adiponectin concentrations at baseline were not associated with change in weight or BMI before or after adjustment for time of follow-up or after additional adjustment for age at follow-up and sex (all P > 0.3). Our data suggest that low plasma adiponectin concentrations do not play an etiologic role in development of obesity in Pima Indians. Therefore, the predictive effect of low plasma adiponectin concentrations on the development of type 2 diabetes seems to be mediated by factors other than increased adiposity.