Many risk factors have been implicated in the pathogenesis of erectile dysfunction (ED), but it is not clearly evident which of these factors are more relevant among the young population. The aim of this project was to find the most significant risk factors for this disease in young patients. We included 434 patients with organic ED younger than 40 years and 272 age-matched controls. All participants had their complete history taken (including the International Index of Erectile Function-5 [IIEF-5]) and underwent physical examination and some laboratory investigations. Univariate analysis was then applied to study the significance of the following factors in the predisposition of ED: smoking, use of recreational drugs, obesity, dyslipidemia, diabetes mellitus, hypertension, coronary heart disease, and chronic pelvic pain syndrome. This analysis showed that smoking, use of recreational drugs, dyslipidemia, hypertension, and obesity were the significant factors (P < .05 for each factor). When these significant factors were studied in the multivariate model, the only factors that sustained the statistical significance were smoking (P < .05; odds ratio [OR], 1.78; 95% confidence interval [95% CI], 1.16-2.72) and use of recreational drugs (P < .05; OR, 3.18; 95% CI, 1.15-8.82). In addition, a negative correlation was detected between the smoking index of the impotent patients and their IIEF-5 score (r(2) = 0.67; P < .05). In conclusion, smoking and the use of recreational drugs are the most significant risk factors for organic ED in patients younger than 40 years.