There has been much interest in the role of dietary factors in the etiology and progression of breast disease. Due to its wide consumption and the many biochemical and physiologic effects it exerts, caffeine has been extensively examined in both clinical and experimental studies. To date, clinical studies investigating a possible relationship between caffeine consumption and breast disease in humans have yielded inconsistent and inconclusive results; further research is needed to resolve this uncertain relationship. In experimental studies utilizing laboratory rats and mice, caffeine has been shown to affect normal, hyperplastic, and carcinomatous mammae development. It has been proposed by many laboratories that antagonism of adenosine receptor is the most plausible mechanism to account for the many biologic activities of caffeine. However, other mechanisms by which caffeine may act cannot be discounted. Further research is needed to affirm the mechanism(s) by which caffeine acts, especially with regard to the developmental growth of normal, benign and carcinomatous human breast tissue.