INTRODUCTION: Little is known about Hypoactive Sexual Desire Disorder (HSDD) in men. AIM: To provide the first comprehensive characterization of men diagnosed with HSDD (Diagnostic and Statistical Manual of Mental Disorders, 4th Edition, Text Revision [DSM-IV-TR]) using established patient-reported outcomes (PROs) and new PROs developed in line with U.S. Food and Drug Administration (U.S. FDA) guidance. METHODS: This 4-week non-treatment study recruited men (N=200) with or without symptoms of low sexual desire and related distress. Men with erectile dysfunction, serum testosterone <300 ng/dL, or depression were excluded. Men completed assessments of sexual desire and sex-related distress and underwent structured clinical interviews for the diagnosis of HSDD. MAIN OUTCOME MEASURES: Primary endpoints were scores on the Sexual Desire Inventory (SDI), Male Desire Scale (MDS), Sexual Concerns Inventory-Male (SCI-M), and Sexual Desire Relationship Distress Scale (SDRDS) on day 28, and University of California, Los Angeles (UCLA) Psychosexual Diary on days 21-27. Scores are presented as median (interquartile range). RESULTS: There were no clinically relevant differences in age, serum testosterone, depressive symptomatology, erectile function, concomitant illness, or medication use between men with HSDD (N=109) and men without HSDD (N=91). However, clinically meaningful differences between men with and without HSDD were observed in sexual desire according to SDI score (40.0 [21.0] vs. 65.0 [25.0]) and MDS sexual desire domain score (18.0 [8.0] vs. 31.0 [13.0]), in sex-related distress according to SCI-M score (22.0 [12.0] vs. 6.0 [12.0]) and SDRDS score (36.0 [17.0] vs. 10.0 [16.0]), and in UCLA Psychosexual Diary sexual activity domain score (2.6 [2.7] vs. 4.9 [3.9]) (P<0.0001, for all). CONCLUSIONS: Based on a brief structured interview, diagnosis according to DSM-IV-TR criteria for HSDD identified a population of men comparable with men without HSDD in age, serum testosterone, concomitant illness and medication use but distinct in their experience of sexual desire and distress associated with low desire. These controlled data characterize HSDD in men as a distinct sexual dysfunction.