Within a 10-year period reconstructive urinary tract surgery has been carried out in eight children with solitary kidneys. The children were 0-5 years old. Six had unilateral renal agenesis and two had unilateral multicystic kidney. In five children ureteroneocystostomy was performed, in two of them because of reflux. In two children pyeloureteroplasty was performed, and in one both ureteroneocystostomy and pyeloureteroplasty. The multicystic kidneys were removed. The renal function was poor preoperatively in five children; two of these also had urosepsis. These children were all under 15 months of age. Postoperatively, the renal function was subnormal (although improved) in two children; in six it was normal. The most important prognostic factors in solitary kidneys with urinary tract obstruction are infection and developmental injury.