X-linked lymphoproliferative syndrome is a well-described syndrome often characterized by progression to fatal infectious mononucleosis. Many mutations of the SH2D1A gene have been identified in patients with X-linked lymphoproliferative syndrome. These mutations are often associated with either decreased or impaired function of the protein product, signaling lymphocytic activation molecule-associated protein. We describe a patient with a novel missense mutation in SH2D1A. We report on his unique presentation, clinical course and subsequent successful treatment with a matched unrelated donor bone marrow transplant.