Adiponectin, an adipocyte-derived serum protein, is known to positively affect the glucose and lipid metabolism and these effects are mediated by its receptors, AdipoR1 and R2. Serum adiponectin levels are inversely associated with breast cancer risk, but the molecular mechanisms underlying this association are not fully elucidated. Thus, the purpose of this study was to investigate the influence of adiponectin on breast cancer cells in vitro. We were able to demonstrate the expression of AdipoR1 and R2 in MCF-7, MDA-MB-231 and SK-BR-3 breast cancer cells on the mRNA level. Furthermore, the AdipoR1 protein could be detected by immunoblot analysis. In MCF-7 breast cancer cells, the expression of AdipoR1 significantly declined after stimulation with 17-beta estradiol, whereas the cyclin A2 expression significantly increased. Both effects were inhibited by the addition of adiponectin. Treatment with different concentrations of adiponectin in steroid-hormone-free medium did not affect cell proliferation or apoptosis. In contrast, after the addition of 17-beta estradiol, adiponectin slightly decreased the growth of the MDA-MB-231 and SK-BR3 cells but increased proliferation of the hormone-dependent MCF-7 breast cancer cells. Adiponectin also triggered cellular apoptosis in MDA-MB-231 breast cancer cells in the presence of 17-beta estradiol. These findings suggest that a cross-talk between adiponectin and estrogen receptor signaling exists in breast cancer cells and that adiponectin effects on the growth and apoptosis of breast cancer cells in vitro are dependent on the presence of 17-beta estradiol.