Background: The metabolic syndrome (MS) might increase the risk of cardiovascular disease in testicular cancer (TC) survivors. We investigated its prevalence, development, vascular implications, and the role of gonadal function. Methods: TC survivors treated with chemotherapy and follow-up >= 3 years (N = 370, study I) were retrospectively evaluated for the development of cardiovascular risk factors. A subgroup followed 3-20 years (N = 173, study II) was compared with controls (N = 1085) for MS prevalence and evaluated for vascular function. Results: In TO survivors (study I), 24% developed overweight, 24% hypercholesterolemia, and 30% hypertension, after median follow-up of 1.7, 0.9, and 5.1 years, respectively. At the median follow-up of 5 years (study II), 25% of survivors have the MS {odds ratio (OR) 2.2, [95% confidence interval (CI) 1.5-3.3] compared with controls}. Survivors with MS have features of inflammation and prothrombotic state, increased carotid artery intima-media thickness. Survivors with testosterone levels <15 nmol/l(22%) have an increased risk of the MS (OR 4.1, 95% CI 1.8-9.3). Conclusions: The current data suggest that the MS occurs at earlier age in TC survivors treated with chemotherapy compared with controls and is accompanied by early signs of atherosclerosis. As low testosterone may have a causal role, it is a target for interventions.