The immunosuppressive treatment with cyclosporin A plus low-dose prednisolone in 33 children after kidney transplantation was compared with conventional treatment with azathioprine plus regular prednisolone dosage in 34 children. The results showed the following: Graft survival in the CyA group is significantly better than in the conventional group (97% vs. 68% at one year). Patient survival is the same in both groups (97% vs. 94%). Kidney function six weeks and one year after successful renal transplantation is significantly lower in the CyA group than in the conventional group. The major nephrotoxic effect of CyA seems to be related to the first period after kidney transplantation, since later the decline in renal function is the same in both treatment groups. Other side effects of CyA are not severe and are well manageable. A major benefit of CyA treatment is the growth after transplantation, which is significantly better than in the conventional group. Almost all transplanted children show normal or even catch-up growth rates.