X-linked severe combined immunodeficiency (SCID) is an inherited disorder of the immune system that occurs almost exclusively in males. Boys with X-linked SCID are prone to recurrent and persistent infections, including infections with organisms that ordinarily do not cause illness in healthy people. Some of these infections can be very serious or life-threatening in boys with X-linked SCID. Many infants with the condition also experience chronic diarrhea and skin rashes, and may grow more slowly than other children. Without treatment, affected males usually live only into infancy.