This report reviews the clinicopathologic, immunologic, and molecular biological features of the congenital immunodeficiencies and their associated lymphoproliferative disorders (LPD) including cases presented at the Third Slide Workshop of the Society of Hematopathology, held in Duarte California, in October 1995. The congenital immunodeficiencies most commonly associated with LPD include Wiskott-Aldrich syndrome (WAS), common variable immunodeficiency (CVID), ataxia telangiectasia (AT), severe combined immunodeficiency (SCID), X-linked lymphoproliferative disorder (XLP), and hyper-IgM syndrome. Each form of immunodeficiency disorder is associated with its own risk factors, which affect the pattern of LPD encountered. AT is characterized by a defect in DNA repair. The lymphomas and leukemias in this syndrome resemble those seen in sporadic LPD, but tend to occur at an earlier age. Epstein-Barr virus (EBV) plays an important role in the LPD associated with many immunodeficiency disorders including WAS, CVID, SCID, and XLP. One should use a combination of clinical, histopathologic and molecular data in the evaluation of lymphoproliferative lesions in this group of patients. Immunophenotypic and molecular evidence of clonality does not necessarily imply an aggressive clinical course, an exemplified by some LPD in WAS, which may show evidence of monoclonality in serum and lymph nodes, and yet still behave in a benign or indolent fashion.