Bronchial-associated lymphoid tissue (BALT) lymphoma is a distinct subgroup of low-grade B-cell extranodal non-Hodgkin's lymphoma, classified as marginal-zone lymphoma. This study was performed in order to assess the natural history of this rare entity. We evaluated retrospectively the clinical data of 22 patients with biopsy-proven BALT lymphoma at two tertiary-care institutions from 1996 to 2002. Immunophenotyping was done to confirm the abnormal populations of B-lymphoid cells in all cases, and clonality was determined by flow cytometry or molecular studies. There were 11 men and 11 women in the sample, median age 61 years (range 21-80 years); nine were asymptomatic at diagnosis. All 13 symptomatic patients had non-specific pulmonary complaints. On computed tomographic examination of the chest, 11 patients had bilateral disease, 12 had lung nodules, and 10 had a mass or air-space consolidation. In all but one case the disease was localised to the lung at diagnosis and none had peripheral blood or bone marrow involvement. Out of 22 patients, 20 received treatment in various combinations, 12 had chemotherapy and/or rituximab, six had surgery, and two received radiation therapy as primary treatment. A complete response (CR) was achieved in nine patients and a partial response was obtained in 10 patients. Seven of 10 patients who had unilateral disease achieved a CR. The estimated progression-free survival was 53 months. All patients were alive during the median follow-up period of 36 months (range 12-76 months). It appears that BALT lymphoma tends to be localised to lung at the time of diagnosis, responds well to local or systemic therapy, and has a favourable prognosis.