Nocturnal enuresis is defined as involuntary wetting while asleep at least twice a week in children over the age of five. Primary nocturnal enuresis describes those children who have always been wet. Secondary nocturnal enuresis is defined as a relapse after a child has been completely dry for at least six months. Up to the age of nine years, nocturnal enuresis is twice as common in boys than girls but thereafter there is no sex difference in prevalence. At the age of five, 2% of children wet every night, and 1% are still wetting every night in their late teens. Bedwetting is not primarily caused by an underlying psychological disorder. However, psychological problems and life events can exacerbate or precipitate bedwetting in susceptible children who have a genetic basis for their condition.