Nocturnal enuresis refers to repeated voiding of urine into clothes or bed that occurs only during sleep (i.e., during the night) in an individual who has reached a developmental age when urinary continence is ordinarily expected (5 years). The urinary incontinence may have been present from birth (i.e., an atypical extension of normal infantile incontinence), or may have arisen following a period of acquired bladder control. In most cases, the behaviour is involuntary but in some cases it appears intentional.