The clinical significance of metabolic syndrome (MetS) versus its single components in erectile dysfunction (ED) is conflicting. Thus, the purpose is to analyze the available evidence on the relationship between MetS-along with its components-and ED. All prospective and retrospective observational studies reporting information on ED and MetS were included. In addition, we here reanalyzed preclinical and clinical data obtained from a previously published animal model of MetS and from a consecutive series of more than 2697 men (mean age: 52.7 ± 12), respectively. Data derived from this meta-analysis showed that MetS was associated with an up to fourfold increased risk of ED when either unadjusted or adjusted data were considered. Meta-regression analysis, performed using unadjusted statistics, showed that the MetS-related risk of ED was closely associated with all the MetS components. These associations were confirmed when unadjusted analyses from clinical models were considered. However, fully adjusted data showed that MetS-associated ED was more often due to morbidities included (or not) in the algorithm than to the MetS diagnostic category itself. MetS is also associated with low testosterone, but its contribution to MetS-associated ED-as derived from preclinical and clinical models-although independent, is marginal. The results of our analysis suggest that MetS is a useless diagnostic category for studying ED. However, treating the individual MetS components is important, because they play a pivotal role in determining ED.