We reviewed our experience with 30 nodal and extranodal lymphoid lesions from 17 patients with common variable immunodeficiency (CVID). Immunohistochemical studies were performed on biopsies from 15 patients, in situ hybridization for Epstein-Barr virus in nine cases, and gene rearrangement analysis on seven lesions. The biopsies were classified into four groups: malignant lymphoma (two cases); atypical lymphoid hyperplasia (eight cases); reactive lymphoid hyperplasia (14 cases); and chronic granulomatous inflammation (six cases). The two malignant lymphomas were diagnosed using histologic criteria; tissue was not available for the assessment of clonality. In one neoplasm, Epstein-Barr virus was identified in the tumor cells by in situ hybridization. The cases of reactive lymphoid hyperplasia and chronic granulomatous inflammation had no atypical architectural, cytologic, or immunohistochemical features. The cases of atypical lymphoid hyperplasia were of particular interest, as these patients had either widespread involvement or massive disease. The diagnosis of lymphoma was considered likely by the clinicians and, in three cases, the histologic slides were originally interpreted as malignant lymphoma by the referring pathologists. Although the architecture of these lesions appeared to be effaced on hematoxylin and eosin-stained sections, immunohistochemical analysis demonstrated preserved architecture with florid expansion of B-cell and T-cell compartments. In addition, clinical follow-up of these patients was benign, and gene rearrangement analysis in three lesions revealed no evidence of clonality. We conclude that the majority of lymphoid lesions in patients with CVID are benign. Immunohistochemical and gene rearrangement studies are particularly helpful in the assessment of cases of atypical lymphoid hyperplasia.