Renal tract malformations are congenital anomalies of the kidneys and/or lower urinary tract. One challenging feature of these conditions is that they can present not only prenatally but also in childhood or adulthood. The most severe types of malformations, such as bilateral renal agenesis or dysplasia, although rare, lead to renal failure. With advances in dialysis and transplantation for young children, it is now possible to prevent the early death of at least some individuals with severe malformations. Other renal tract malformations, such as congenital pelviureteric junction obstruction and primary vesicoureteric reflux, are relatively common. Renal tract malformations are, collectively, the major cause of childhood end-stage renal disease. Their contribution to the number of adults on renal replacement therapy is less clear and has possibly been underestimated. Renal tract malformations can be familial, and specific mutations of genes involved in renal tract development can sometimes be found in affected individuals. These features provide information about the causes of malformations but also raise questions about whether to screen relatives. Whether prenatal decompression of obstructed renal tracts, or postnatal initiation of therapies such as prophylactic antibiotics or angiotensin blockade, improve long-term renal outcomes remains unclear.