PURPOSE: We evaluated the contributing factors and etiology of erectile dysfunction (ED) in unmarried men. MATERIALS AND METHODS: From March 1998 to December 2001, we examined 49 unmarried men age 21 to 44 years (mean 29 years) with ED. All patients were assessed by history, physical examination, laboratory studies, combined intracavernous injection and stimulation test (CIS test), penile duplex ultrasonography, and other indicated tests to identify the etiology of erectile dysfunction. RESULTS: The majority of patients had vasculogenic impotence (arteriogenic 26.5%; venogenic 14.3%; mixed 16.3%). Less common were psychogenic (26.5%), hormonal (6.1%), neurogenic (8.1%), and other causes (2.0%). Contributing factors were present in 71.4% of patients, such as penile blunt trauma in 22 patients (44.9%), genitourinary disease in 14 (28.6%), substance abuse in 7 (14.3%), and medical illness in 5 (10.2%). CONCLUSIONS: Erectile dysfunction in unmarried men generally is vasculogenic in origin, and penile blunt trauma is the most common contributing factor.