An update of the pathogenesis and treatment of monosymptomatic bedwetting is presented. This frequently occurring entity seems to have a multifactorial pathogenesis incorporating arousal disturbances and disturbances to the circadian rhythm of diuresis modulating hormones. It has recently been substantiated that the bladder reservoir function in monosymptomatic bedwetting is normal. This is further underlined by the fact that treatment of instability of the bladder has proven futile. In a substantial part of the monosymptomatic bedwetters the changes in circadian rhythm of antidiuretic hormone can be counteracted by desmopressin diacetate (DDAVP), which abolishes the symptom in more than 2/3 of the patients. Monitoring circadian rhythms of arginine vasopressin (AVP) and treatment with DDAVP have led to increased understanding of the pathogenesis of monosymptomatic bedwetting and opened new fields of investigation.