OBJECTIVE To test the recent hypothesis that lymphomatoid granulomatosis (LYG) is a clonal B-cell proliferative process related to Epstein-Barr virus (EBV). METHODS Historically, LYG has been classified as an angiocentric T-cell lymphoproliferative disorder. To further characterize LYG in the skin, we analyzed for EBV RNA in lymphocytes using in situ hybridization, coupled with colabeling for B-cell and T-cell markers. Clonality of lymphocytes was assessed by polymerase chain reaction using primers for immunoglobulin heavy chain genes and T-cell receptor beta and gamma genes. METHODS Academic referral center. METHODS In a 5-year retrospective review, we identified 4 patients with classic clinical and pathologic features of LYG in skin and lung, and tissue available from both sites. METHODS The presence or absence of EBV RNA and clonal gene rearrangements in cutaneous and pulmonary lesions of LYG. RESULTS Biopsy specimens of skin and lung in all patients revealed angiocentric infiltrates predominantly composed of T lymphocytes. Epstein-Barr virus RNA was identified in the skin of 1 patient and the lung of 3 patients, and was restricted to B cells. Polymerase chain reaction revealed clonal immunoglobulin heavy chain gene rearrangements and no clonal rearrangement of T-cell receptor genes in skin and lung tissue of all patients. CONCLUSIONS At least some examples of LYG in the skin and lung are characterized by a clonal proliferation of B lymphocytes, some of which contain EBV RNA. The B cells are typically scarce and may be obscured by striking angiocentric T-cell infiltrates.