Mucosa-associated lymphoid tissue (MALT) is a specialized form of lymphoid tissue that may be acquired at sites in response to chronic inflammation. Most low-grade, B-cell, non-Hodgkin lymphomas that occur at extranodal sites derive from acquired MALT. Confusing and overlapping terms have been used to describe these lymphomas, but immunohistochemical advances now allow more precise subtyping. Our review of the literature yielded only 2 previous reports of sinonasal MALT-derived lymphoma, and we report an additional case in a patient with a history of chronic sinusitis. Current developmental theories of MALT-derived lymphomas are discussed. In addition, we review the clinical, histologic, and immunophenotypic features of MALT-derived lymphomas.