OBJECTIVE Giant lamellar bodies (GLBs) are rare pulmonary inclusions, most frequently described in sclerosing haemangiomas. Following a recent report of their presence in a case of pulmonary lymphoma of MALT origin, our aims were to determine their frequency in pulmonary lymphoproliferative disorders, examine their structure and investigate their aetiology further. RESULTS We reviewed a series of 29 pulmonary lymphomas (23 low-grade, six high-grade) and 18 cases of reactive pulmonary lymphoid hyperplasia. Five of 23 (22%) low-grade lymphomas contained GLBs, 4/4 of which stained for surfactant apoprotein A but not for surfactant apoprotein B. No GLBs were seen in 18 cases of reactive pulmonary lymphoid hyperplasia or six high-grade primary pulmonary lymphomas. Ultrastructural examination revealed concentrically arranged extracellular material forming roughly spherical structures up to 25 microm in diameter. The GLBs were often surrounded by foamy cells and cholesterol clefts, supporting an origin, at least in part, from products of cell breakdown and surfactant degradation. CONCLUSIONS These findings support the idea that the presence of lamellar bodies is in part due to stasis of products arising from degradation of surfactant, in association with certain types of chronic pulmonary pathology. Given their absence in reactive pulmonary lymphoid hyperplasia, the presence of GLBs as an epiphenomenon in a pulmonary lymphoid infiltrate should warrant careful investigation with regard to the diagnosis of low-grade MALT lymphoma.