Low plasma adiponectin has been identified as a risk factor for type 2 diabetes. Our objective was to determine the extent to which low maternal plasma adiponectin is predictive of gestational diabetes mellitus (GDM), a condition that is biochemically and epidemiologically similar to type 2 diabetes. We used a prospective, nested case-control study design to compare maternal plasma adiponectin concentrations in 41 cases with 70 controls. Subjects were selected from a population of 968 women who provided blood samples in early pregnancy. Plasma adiponectin was determined using an ELISA. Adiponectin concentrations were statistically significantly lower in women with GDM than controls (4.4 vs. 8.1 micro g/ml, P < 0.001). Approximately 73% of women with GDM, compared with 33% of controls, had adiponectin concentrations less than 6.4 micro g/ml. After adjusting for confounding, women with adiponectin concentrations less than 6.4 micro g/ml experienced a 4.6-fold increased risk of GDM, as compared with those with higher concentrations (95% confidence interval, 1.8-11.6). Our findings are consistent with other reports suggesting an association between hypoadiponectemia and risk of type 2 diabetes. Our findings extend the literature to include GDM. Studies designed to examine the effect of dietary and pharmacological mediators of adiponectin concentrations in pregnant and nonpregnant subjects are warranted.