['To investigate the incidence of nocturnal enuresis post-cardiac transplantation.', 'Seventy two cardiac transplantations have been performed in children under 16 years of age. All recipients who were alive and over 4 years of age at the time of the study received a questionnaire about urinary symptoms; 54 of the 57 eligible children participated.', 'Twenty five children had persistent nocturnal enuresis post-transplantation. Thirteen of them had previously attained reliable night-time dryness but developed secondary nocturnal enuresis following transplantation, with three subsequently regaining dryness at ages 8, 12, and 17 years; 10 were still wetting mean age 12.3. Twelve children had not achieved night-time dryness when transplanted (all were under 4 years of age at the time) and continued to wet. Only one of these children achieved dryness (at age 12 using oxybutynin); the other 11 remained wet at night at a mean age of 9.3 years. Twenty nine children were dry at night post-transplantation, but 21 of them had nocturia at least three times a week. There is a significant difference in age at transplantation between the primary nocturnal enuretic children (mean age 2.0) and the secondary nocturnal enuretic children (mean age 7.4) as well as between the primary nocturnal enuretic children and the non-enuretic children (mean age 9.0).'] Is nocturnal enuresis a common complication following cardiac transplantation?