Adiponectin is an adipokine with profound antidiabetic and antiatherogenic effects. Circulating adiponectin concentrations are higher in women than in men. In order to study the molecular aspects of this sex-specific dimorphism, we examined the expression of adiponectin in human fat cells under the influence of sex hormones, using SGBS cells as an in vitro model. Androgen and estradiol receptor 1 and 2 (AR, ESR1, ESR2) mRNA expression increased dramatically during adipogenic differentiation. Stimulation with human male and female serum led to a downregulation of adiponectin expression, with male serum exerting significantly stronger inhibitory properties than female serum (p<0.05). Increasing concentrations of testosterone or estradiol influenced neither adiponectin mRNA expression and secretion nor intracellular protein expression of high-, middle-, and low-molecular-weight (HMW, MMW, LMW) adiponectin multimers. These data have been verified in in vitro-differentiated primary human adipocytes. We conclude that although human adipocytes express AR, ESR1, and ESR2 and respond to testosterone treatment with a decrease in leptin expression, expression and secretion of adiponectin is unaffected by sex steroids. We hypothesize, therefore, the existence of a serum factor that is differently regulated by sex steroids and subsequently causes the sex dimorphism in circulating adiponectin levels.