The present study was conducted to determine whether the usual temporal relationship between rapid eye movement and penile tumescence was present in a group of narcoleptic patients who had demonstrated the abnormal phenomenon of sleep onset rapid eye movement. We studied 5 men with a clinical history of sleep attacks and at least 1 auxiliary symptom of narcolepsy. Results indicated that penile tumescence occurred during temporally normal and abnormal rapid eye movement sleep. These findings provide further evidence of the strong temporal relationship between rapid eye movement sleep and penile tumescence.