Mucosa-associated lymphoid tissue (MALT) lymphomas are indolent neoplasms which tend to remain localized for a long time before spreading. We describe here the case of a 36-year-old woman with a low-grade MALT lymphoma involving the lung, stomach, lingual tonsil, and bone marrow at the time of diagnosis. The clonal origin of the pulmonary and bone marrow neoplastic infiltrates was assessed by means of gene rearrangement analysis. All of the involved sites were infiltrated by centrocyte- and monocytoid-like cells expressing the B-cell-associated antigens CD19 and CD20 and showed IgM lambda chain restriction; no CD5, CD10, or CD43 expression was detectable. As the patient had a history of recurrent bronchitis, and computed tomography performed 3 years before the lymphoma diagnosis had already revealed a lesion of the left lung, we conclude that the present case probably represents a pulmonary low-grade MALT lymphoma characterized by an early and unusual involvement of different mucosal sites and bone marrow.