Introduction: Low testosterone levels in men are associated with the metabolic syndrome (MetS) as well as with depressive symptoms, low vitality, and sexual dysfunction. Aim: To assess the effects of testosterone administration on these subjective symptoms, which have not extensively been studied in hypogonadal men with the MetS. Main Outcome Measures: The Beck Depression Inventory (BDI-IA), Aging Males' Symptoms (AMS) scale, and International Index of Erectile Function 5-item (IIEF-5) scale at baseline, 18 and 30 weeks were analysed using multilevel analysis. Methods: In a randomized, placebo-controlled, double-blind, phase III trial (ClinicalTrials.gov identifier: NCT00696748), 184 men suffering from both the MetS and hypogonadism were included. They were treated for 30 weeks with either parenteral testosterone undecanoate (TU; 1,000 mg IM TU, at baseline, and after 6 and 18 weeks; Nebido®) or placebo injections, 105 (92.9%) men receiving TU and 65 (91.5%) receiving placebo completed the 30-week trial. Results: The 184 men were aged mean 52.1 years old (standard deviation [SD] 9.6; range 35-69), with a mean body mass index of 35.5 kg/m2 (SD 6.7; range 25.1-54.8), and a mean total testosterone level of 8.0 nmol/L (SD 4.0). There were significant improvements in BDI-IA (mean difference vs. placebo after 30 weeks: -2.5 points; 95% confidence interval [CI]: -0.9; -4.1; P = 0.003), AMS (-7.4 points; 95% CI: -4.3; -10.5; P < 0.001), and IIEF-5 (+3.1 points; 95% CI: +1.8; +4.4; P < 0.001). The effects on the BDI-IA, AMS, and IIEF-5 were strongest in men with baseline total testosterone levels <7.7 mmol/L (i.e., median value). Conclusions: TU administration may improve depressive symptoms, aging male symptoms and sexual dysfunction in hypogonadal men with the MetS. The beneficial effects of testosterone were most evident in men with the lowest baseline total testosterone levels. © 2010 International Society for Sexual Medicine.