Several adipocytokines, such as leptin or adiponectin, are associated with obesity and the risk for breast cancer. Adiopcyte fatty acid binding-protein (A-FABP) is another protein found in adipose tissue; therefore, we investigated the association of A-FABP with the occurrence and prognosis of breast cancer. In our study, 200 women attending the University of Ulm for breast surgery between the years 2005 and 2007 were included; 159 had histologically confirmed breast cancer; 41 had histologically confirmed benign lesions. Serum levels of A-FABP, leptin, and adiponectin were measured, and their relationship to body-mass-index (BMI), breast cancer, and tumor characteristics were analyzed; logistic regression model was adjusted to age, BMI, menopausal status, use of Hormone Replacement Therapy (HRT), and family history of breast cancer. Serum A-FABP levels were found to be significantly higher in obese (BMI C 25) than in non-obese women (BMI B 24.9), 41.16 ng/ml and 24.95 ng/ml, respectively (P \ 0.0001). Independent of obesity, the serum A-FABP levels were significantly higher in breast cancer patients (34.65 ng/ml) than in healthy controls (24.47 ng/ml), P \ 0.0001; the odds ratio (1.038, P \ 0.05, 95% confidence interval 1.001-1.72) showed a significant association of A-FABP with breast cancer risk. Serum leptin levels showed a strong correlation with BMI (r s = 0.78) and were significantly higher in breast cancer patients (20.87 ng/ml) than in controls (14.90 ng/ml), P \ 0.05. In contrast, adiponectin showed no significant association with breast cancer. Concerning tumor characteristics, A-FABP was positively connected with tumor size (T C 2 cm, P \ 0.05) and nodal-status (P \ 0.05). Our study reveals that high A-FABP serum levels are associated with obesity, breast cancer risk, and adverse tumor characteristics.