Résumé : Objectives: The association of low testosterone level and erectile dysfunction (ED) with metabolic syndrome (MS) is receiving increasing attention. The present study determined the psychobiologic characteristics of sexual dysfunction (SD) associated with MS (as defined by the National Cholesterol Education Program's Adult Treatment Panel III criteria) in a series of 803 consecutive male outpatients. Methods: Several hormonal, biochemical, and instrumental (penile Doppler ultrasound [PDU]) parameters were studied, along with general psychopathology scores (Middlesex Hospital Questionnaire modified [MHQ]). The Structured Interview on Erectile Dysfunction (SIEDY) was also applied. Results: Among the 236 patients (29.4%) diagnosed as having a MS, 96.5% reported ED, 39.6% hypoactive sexual desire (HSD), 22.7% premature ejaculation, and 4.8% delayed ejaculation. Patients with MS were characterised by greater subjective (as assessed by SIEDY) and objective (as assessed by PDU) ED and by greater somatised anxiety than the rest of the sample. The prevalence of overt hypogonadism (total testosterone <8 nM) was significantly higher in patients with MS. Among MS components, waist circumference and hyperglycaemia were the best predictors of hypogonadism. Hypogonadal patients with MS showed higher gonadotropin and lower free testosterone levels, suggesting a primary hypogonadism. Among patients with MS, hypogonadism was present in 11.9% and 3.8% in the rest of the sample (p < 0.0001) and was associated with typical hypogonadism-related symptoms, such as hypoactive sexual desire, low frequency of sexual intercourse, and depressive symptoms. Conclusions: Our data suggest that MS is associated with a more severe ED and induces somatisation. Furthermore, MS is associated with a higher prevalence of hypogonadism in patients with SD. The presence of hypogonadism can further exacerbate the MS-associated sexual dysfunction, adding the typical hypogonadism-related symptoms (including HSD, 66.7%). Recognising MS associated with hypogonadism is important for both sexual and general health and its serious potential associated risks. © 2006 European Association of Urology.