Aim of the study was to evaluate whether endothelial dysfunction is a marker of erectile dysfunction (ED) in recreational drug abuse. Sixty-four non-consecutive men complaining of ED from at least 3 months were included. All patients underwent detailed history about recreational drug abuse and were then submitted to dynamic penile duplex ultrasound (PDU). According to pharmaco-stimulated peak systolic velocity (PSV) cutoff at 35 cm s(-1), patients were divided into two groups: organic (O; n=30) and non-organic (NO; n=34) ED. All subjects and 7 healthy age-matched subjects as controls, underwent veno-occlusive plethysmography (VOP) for the evaluation of endothelium-dependent dilatation of brachial arteries. Blood pressure, total and free testosterone, prolactin, estradiol, low-density lipoprotein and high-density lipoprotein cholesterol were also evaluated; patients were classified with regard to insulin resistance through the HOMA-IR index. Cannabis smoking was more frequent in O-ED vs NO-ED (78% vs 3%, P<0.001) in the absence of any concomitant risk factor or comorbidity for ED. VOP studies revealed impaired endothelium-dependent vasodilatation in O-ED but not in NO-ED and controls (12+/-6 vs 32+/-4 and 34+/-5 ml min(-1), respectively; P=0.003). Overall patients showed a direct relationship between HOMA-IR and PSV (r(2)=0.47, P<0.0001), which was maintained in men with organic ED (r(2)=0.62, P<0.0001). In cannabis consumers, a direct relationship between HOMA-IR and VOP was also found (r(2)=0.74, P<0.0001). Receiver-operating characteristic (ROC) curve analysis revealed that VOP values below 17.22 ml min(-1) were suggestive for vasculogenic ED. We conclude that early endothelial damage may be induced by chronic cannabis use (and endocannabinoid system activation); insulin resistance may be the hallmark of early endothelial dysfunction and may concur to determine vascular ED in the absence of obesity. Further studies are warranted to establish a direct relationship between cannabis abuse, onset of insulin resistance and development of vascular ED.