This review is meant to show that all approaches other than the use of genotypically or phenotypically identical family donors for bone marrow transplantation aimed at the treatment of SCID leave a lot of unsolved questions open. The results are inconsistant but successful cases have been reported with the various methods. More children with this disease will be born since there is no way at present time to define heterozygous carriers for most defects. Their treatment remains a challenge for modern pediatrics and immunology. The past has shown that it is worthwile to try known as well as yet unknown approaches to save the life of these children. One of the important side-effects will be a better understanding of the immune system and its development.