This study assessed characteristics of sexual dysfunction in sleep apnea and the efficacy of treatment with continuous positive airway pressure (CPAP). Twenty-two men with sleep apnea syndrome and also sexual dysfunction served as subjects in this study. Tests included physical, psychological, neurological, and penile vascular examinations, along with polysomnography, nocturnal penile tumescence (NPT), and penile rigidity. All patients clinically had a history of snoring and difficulty getting and maintaining erections. Results indicate that erectile dysfunction in patients with sleep apnea could be related to patient's age and chronic cerebral hypoxia due to apnea. Treatment with CPAP relieved erectile dysfunction in one-third of these patients.