This article is a review of the characteristics of bilateral breast cancer (BBC). Synchronous bilateral breast cancer (SBBC) and metachronous bilateral breast cancer (MBBC) account for 2.9-3.9% and 4.1-4.6% of all new breast cancer cases, respectively. The risk factors for SBBC include older patient age and lobular histology. On the other hand, younger age, lobular histology, and positive family history (or genetic factors) are the risk factors for MBBC. Contralateral prophylactic mastectomy in patients with mutations in the