A Cochrane review included 35 studies with a total of 4 768 subjects. The median study duration was six months (range 1.5 to 24 months). The addition of testosterone to hormone therapy (HT) regimens improved sexual function scores for postmenopausal women (SMD 0.41; 95% CI 0.19 to 0.63, for the composite sexual function score; 3 studies, n=330). Significant adverse effects were decreased high-density lipoprotein (HDL) cholesterol levels and an increased incidence of facial hair growth (Peto OR 1.52, 95% CI 1.07 to 2.17; 7 studies, n= 2127) and acne (Peto OR 1.51, 95% CI 1.07 to 2.14; 7 studies, n= 2127). The discontinuation rate was not significantly greater with the addition of testosterone therapy (OR 0.99, 95% CI 0.83 to 1.19; 21 studies, n= 3124). There was no convincing evidence for testosterone effects on sense of wellbeing, unexplained fatigue, bone health, body composition, menopausal symptoms, cognition, or hostility. Evidence on long-term effects with respect to breast cancer and coronary heart disease is lacking.