Adiponectin is an important adipokine exclusively secreted from adipose tissue. Growing evidence suggests that adiponectin inhibits the growth of cancer cells and reduces cancer risk. Many studies have examined the association between circulating adiponectin levels and the risk of breast cancer. However, the results of numerous epidemiological studies have been inconsistent. The aim of the present study was to conduct a systematic review and a meta-analysis on the association between circulating adiponectin levels and the risk of breast cancer. PubMed, MEDLINE, EMBASE, and ISI Web of Science were searched to identify all observational studies that examined the relationship between circulating adiponectin and breast cancer. Standard mean difference (SMD) values and 95% confidence intervals (CIs) were estimated and pooled using the meta-analysis methodology. Summary effect estimates were derived using a random effects meta-analysis model. The analysis included eight studies that met the study criteria and described the relationship between circulating adiponectin levels and breast cancer. A total of 1803 participants and 885 cases of breast cancer were included in this meta-analysis. Serum total adiponectin concentrations were lower in patients with breast cancer, with a pooled SMD of −0.39 μg/ml (95% CI −0.618 to −0.161, P=0.001). However, adiponectin levels were not associated with the risk of breast cancer in premenopausal women [four studies, random effects SMD=0.02 μg/ml (95% CI −0.164 to 0.204, P=0.829)]. These results collectively suggest that lower adiponectin levels are associated with a higher risk of breast cancer in postmenopausal women.