Cutaneous B-cell infiltrates showing a prominent follicular growth pattern with germinal centers are thought by some authors to represent either marginal zone lymphomas with reactive germinal centers or pseudolymphomas. To establish whether a true primary cutaneous follicular lymphoma exists, we studied biopsies from 15 patients with skin lesions characterized histopathologically by the presence of B-cell infiltrates with follicular pattern. Staging investigations, including bone marrow biopsy, were negative in all patients. All were negative for bcl-2 protein expression and did not present the t(14;18). In all biopsy specimens neoplastic follicles showed 1 or more morphologic or immunophenotypic criteria of malignancy (presence of a reduced mantle zone, absence of tingible body macrophages, reduced proliferation rate). In 9 specimens a monoclonal rearrangement of J(H) genes could be detected by polymerase chain reaction analysis. After laser beam microdissection, a band of the same length could be observed in 6 probes from different follicles from the same specimen, indicating the presence of the same monoclonal population of follicle center cells. Follow-up examinations in all patients revealed no evidence of extracutaneous spread (mean follow-up, 48.7 months). Our study demonstrates that primary cutaneous follicular lymphoma represents a distinct entity of the cutaneous B-cell lymphomas. (Blood. 2000;95:3922-3928)