To examine whether circulating total and high-molecular weight (HMW) adiponectin concentrations, measured before pregnancy, are associated with subsequent risk of gestational diabetes mellitus (GDM). This was a nested case-control study among women who participated in the Kaiser Permanente Northern California Multiphasic Health Check-up exam (1984-1996) with a serum sample obtained and who had a subsequent pregnancy (1984-2009). Eligible women were free of recognized diabetes. Case subjects were the 256 women who developed GDM. Two control subjects were selected for each case and matched for year of blood draw, age at exam, age at pregnancy, and number of intervening pregnancies. Compared with the highest quartile of adiponectin, the risk of GDM increased with decreasing quartile (odds ratio [OR] 1.5 [95% CI 0.7-2.9], 3.7 [1.9-7.2], and 5.2 [2.6-10.1]; P(trend) <0.001) after adjustment for family history of diabetes, BMI, parity, race/ethnicity, cigarette smoking, and glucose and insulin concentrations. Similar estimates were observed for HMW (P(trend) <0.001). The combined effects of having total adiponectin levels below the median (<10.29 mg/mL) and being overweight or obese (BMI ?25.0 kg/m(2)) were associated with a sevenfold increased risk of GDM compared with normal-weight women with adiponectin levels above the median (OR 6.7 [95% CI 3.6-12.5]). Prepregnancy low adiponectin concentrations, a marker of decreased insulin sensitivity and altered adipocyte endocrine function, is associated with reduced glucose tolerance during pregnancy and may identify women at high risk for GDM to target for early intervention.