Introduction Testosterone deficiency and metabolic syndrome (MetS) are strongly associated. Patients consulting for sexual dysfunction may have testosterone deficiency, providing a valuable opportunity to assess MetS. The identification of variables predicting MetS is of great importance. AimsTo identify cardiovascular comorbidities and risk factors, including erectile dysfunction (ED), associated with MetS in men aged 45 with total testosterone (TT)<8nmol/L (or <12nmol/L when calculated free testosterone was<250pmol/L) and to gain further insight into the relationship between both conditions. MethodsData were collected from a multicenter, cross-sectional, observational study conducted in Spain among men visiting men's health-care offices with a confirmed diagnosis of testosterone deficiency. Subjects with data for MetS assessment were included in this analysis. Other data available were anthropometrics, toxic habits, cardiovascular comorbidities, ED diagnosis, and TT values. Main Outcome MeasuresThe MetS harmonized definition was used. Waist circumference threshold was 94cm. ED was diagnosed and classified using the International Index of Erectile Function-5 (IIEF-5) questionnaire. Bivariate and multivariate logistic regression analyses were performed to calculate odds ratios (ORs) for MetS. Results Mean age was 61.28.1 years. Prevalences of ED and MetS were 97.6% and 69%, respectively, both increasing with age. Bivariate analysis showed that moderate or severe ED, obesity, and peripheral vascular disease (PVD) were the variables associated with the greatest odds of MetS (OR=2.672 and 2.514, respectively), followed by alcohol intake (OR=1.911). Tobacco use, ag,e and testosterone deficiency severity had a minimal effect that disappeared on multivariate analysis. Elevated triglycerides and HDL-cholesterol were MetS risk factors associated with a lower TT level. Conclusion The high prevalence of MetS among men with testosterone deficiency highlights the opportunity to assess cardiovascular health in patients consulting for sexual dysfunction. Moderate to severe ED, obesity, PVD, and alcohol intake significantly increase the likelihood of MetS. Garcia-Cruz E, Leibar-Tamayo A, Romero J, Piqueras M, Luque P, Cardenosa O, and Alcaraz A. Metabolic syndrome in men with low testosterone levels: Relationship with cardiovascular risk factors and comorbidities and with erectile dysfunction. J Sex Med 2013;10:2529-2538.