Sleep related painful erection is a parasomnia occurring during rapid eye movement (REM) sleep. It is rarely dealt with in the literature, and is very often poorly understood. Because of repeated awakenings, it is interpreted as insomnia, and is attributed to anxiety. EEG recordings associated with nocturnal penile tumescence monitoring indicate the existence of disturbed sleep organization, with awakenings during REM sleep and frequent nocturnal erections, often unrelated to REM sleep. Though the pathophysiological mechanisms involved are not yet understood, an interpretation of sleep-related painful erections is proposed, based on the current understanding and physiology of diurnal and nocturnal erections.