Congenital immune deficiency states have often been valuable experimental models of nature that have significantly enhanced our understanding of the immune response. The relationship between CD4+, CD25+ and Treg cells in the induction of autoimmunity has attracted significant attention. We report herein a male child of consanguineous parents who developed at six months recurrent infections, and at age 5 years, liver dysfunction with serological expression of primary biliary cirrhosis (PBC), an autoimmune liver disease that usually affects middle-aged women. Histologically, there was intense mononuclear cell lymphoid infiltration of the intrahepatic portal tracts, CD3+CD4+T cell lymphopenia in blood and serum antibody to PDC-E2. Peripheral blood lymphocytes were completely deficient of the alpha subunit of the IL-2 receptor (IL-2Ralpha, CD 25), a marker for regulatory T cells (Tregs). Allogenic stem cell transplantation led to full recovery. This case illustrates the role of deficiency of CD4+CD25+ Treg cells in causing autoimmunity, and speaks to the potential use of allogenic stem cell transplantation for immunoreconstitution in adult PBC.