Objectives: Breast and colon cancer are neoplasms well known to be related to obesity. Adiponectin, a protein that increases in obesity, seems to be involved in the relationship but clinical data are limited. Methods: In this study, we therefore evaluated the serum adiponectin levels in 87 breast and 27 colon cancer patients and assessed the relation with BMI, menopausal status, receptor status and stage of disease. Results: Serum adiponectin levels were lower in cancer cases (8583 ± 2095 ng/ml for breast cancer, 9513 ± 2276 for colon cancer) than in controls (13905 ± 3263). Conclusion: A low serum adiponectin level may be associated with both breast and colon cancer, and that this association is not statistically significant for either receptor or menopausal status in breast cancer groups.