This study was designed to determine the effectiveness of desmopressin in the treatment of adolescent nocturnal enuresis and factors that may predict responsiveness. Eighteen adolescents (14 boys, 4 girls) with monosymptomatic nocturnal enuresis were treated with oral desmopressin for three months, starting with 0.2 mg at night and controlling the symptoms every two weeks. After this period, desmopressin was used every other day and the dose was reduced gradually. The treatment was completed at the end of six months. As factors that may predict response before treatment, a range of variables (family history of enuresis, educational levels of parents, number of children, first child in family, birth weight) and urine osmolality was evaluated. Disappearance of bedwetting by using desmopressin has been observed in adolescents who have a high urine osmolality. We did not observe any relapse during reducing desmopressin dose gradually, but on complete cessation of the treatment, relapses were seen. Six months after the end of the therapy, we could not find any patient who recovered completely. Desmopressin seems to be effective in the treatment of primary nocturnal enuresis while on therapy but during the long-term follow-up, all cases relapsed.