© 2014 John Wiley & Sons Ltd. Context The effects of testosterone treatment on glucose metabolism and other outcomes in men with type 2 diabetes (T2D) and/or the metabolic syndrome are controversial. Objective To perform a systematic review and meta-analysis of placebo-controlled double-blind randomized controlled clinical trials (RCT) of testosterone treatment in men with T2D and/or the metabolic syndrome. Data sources A systematic search of RCTs was conducted using Medline, Embase and the Cochrane Register of controlled trials from inception to July 2014 followed by a manual review of the literature. Study selection Eligible studies were published placebo-controlled double-blind RCTs published in English. Data extraction Two reviewers independently selected studies, determined study quality and extracted outcome and descriptive data. Data synthesis Of the 112 identified studies, seven RCTs including 833 men were eligible for the meta-analysis. In studies using a simple linear equation to calculate the homeostatic model assessment of insulin resistance (HOMA1), testosterone treatment modestly improved insulin resistance, compared to placebo, pooled mean difference (MD) -1·58 [-2·25, -0·91], P <0·001. The treatment effect was nonsignificant for RCTs using a more stringent computer-based equation (HOMA2), MD -0·19 [-0·86, 0·49], P = 0·58). Testosterone treatment did not improve glycaemic (HbA1c) control, MD -0·15 [-0·39, 0·10], P = 0·25, or constitutional symptoms, Aging Male Symptom score, MD -2·49 [-5·81, 0·83], P = 0·14). Conclusions This meta-analysis does not support the routine use of testosterone treatment in men with T2D and/or the metabolic syndrome without classical hypogonadism. Additional studies are needed to determine whether hormonal interventions are warranted in selected men with T2D and/or the metabolic syndrome.