Testosterone supplementation can be considered as a treatment option for surgically postmenopausal women with a distressful low sexual desire disorder, while on oestrogen therapy with or without progestagens. The purpose of this study is to review the available clinical data on the impact of exogenous testosterone containing postmenopausal hormone therapy on breast cancer risk. A literature search was done in MEDLINE (1969-July 2007) and in addition in EMBASE and Biosis (1990-July 2007) for original reports in English and French. Case reports and studies without a control group were excluded. No prospective randomized clinical trials were found. The five studies found (two case-control studies, two cohort studies and one retrospective observational study) showed inconsistent results. All studies had severe methodological limitations. Formulations and dosages used could be considered suboptimal. At present, there are no valid randomized or observational clinical studies that provide evidence that the addition of testosterone to conventional postmenopausal hormone therapy influences breast cancer risk.