There is no safe and effective treatment for DiGeorge syndrome and most patients die by the age of two. Complete DiGeorge syndrome is characterized by very low T cell or very low naïve T cell numbers. In this study, typical complete DiGeorge syndrome subjects received human postnatal cultured thymus tissue transplants. Thymus tissue that would otherwise be discarded was transplanted into DiGeorge subjects in the operating room. At the time of transplantation, a skin biopsy was obtained to look for any preexisting T cells. After transplantation, subjects were followed by routine research immune evaluations, using blood samples obtained every 2-4 weeks. At approximately 2-3 months post-transplantation subjects underwent an open biopsy of the allograft. The biopsy was done under general anesthesia in the operating room. At the time of the graft biopsy, another skin biopsy was obtained to look for clonal populations of T cells.