Marginal zone lymphoma (MZL) is a distinct entity among B-cell lymphomas. We report on a 53-year-old woman who developed disseminated primary cutaneous MZL with secondary lymph node involvement and perinodular spreading. The tumor cell phenotype was characterized as CD20/CD79a/kappa/lambda+/ bcl-2-positive, CD3/5/15/39/bcl-1-negative. Ki-67 was expressed by 20-35% of tumor cells. There was no evidence of systemic (including bone marrow) involvement. The diagnosis of MZL with plasmacellular differentiation (Stage IVa) was made. The patient was treated with interferon alpha2a injected s.c. at 9x10(6) U 3 days a week for 1 year. During this time the skin lesions completely disappeared. No evidence of lymph node or extracutaneous disease was found. The patient remains in complete remission. Side effects were only of grade I (WHO); the Karnovsky index was 90%. As shown for other types of primary cutaneous B-cell lymphoma, prolonged interferon alpha monotherapy may be effective in controlling the disease and/or inducing complete remission in MZL.