For most autoimmune disorders, the pattern of inheritance is very complex. The major histocompatibility complex (MHC) gene complex has been implicated as the major genetic component in the predisposition to these diseases but other genes are likely to be involved. Based on function and experimental data, the gene encoding cytotoxic T lymphocyte-associated antigen 4 (CTLA4) has been suggested as a candidate gene for conferring susceptibility to autoimmunity. In this review, we critically evaluate the evidence for pathogenetical involvement of CTLA-4 in the different autoimmune diseases with focus on the possible role of genetic variation of the CTLA4 locus.