Nocturnal enuresis is a problem which affects a significant number of children in the developmental period. The diagnostic work-up should be completed if the condition does not resolve after five years of age or in older children who experience a recurrence of nocturnal enuresis. This case report presents a 12-year-old boy with nocturnal enuresis secondary to hyperthyroidism. In many cases, nocturnal enuresis is linked to emotional disorders (like school or family problems), but increasingly the condition is rather a consequence than the reason. Currently, nocturnal polyuria, inadequate capacity of the urinary bladder and functional urinary tract disorders are considered to be the most common causes of nocturnal enuresis. It happens, however, that the background of bedwetting is more complex and the diagnosis is not so obvious.