Congenital megaureter in a solitary kidney (CMSK) is a life-threatening disease. From January 1988 to December 1993, we treated 9 patients for CMSK (2 cases with unilateral renal dysplasia and 7 with unilateral renal agenesis). In 7 cases, the malformation was detected by prenatal ultrasonography and urological counseling. The ages at first postnatal observation ranged from 24 h to 5 years (mean = 8 months). The postnatal urological workup included: serum renal function screening, urinary system ultrasonography, a micturition cystogram, intravenous pyelography and a nuclear renal scan. The therapy of choice was decided on the basis of renal function. One emergency divertive procedure was performed after birth, in 3 cases of renal failure in the first 2 weeks of life. The remaining cases were operated electively at an average age of 20 months. In 2 cases that underwent delayed surgical elective correction and in 1 of the 3 cases that underwent an emergency diversion, some degree of renal failure still persists. In our opinion, prenatal diagnosis, accurate postnatal urological workup and strict postoperative follow-up are fundamental to avoid the devastating consequences of CMSK on the affected child.