The clinical and pathologic findings in 36 patients with primary pulmonary non-Hodgkin's lymphoma were retrospectively evaluated. Each lymphoma was classified according to the Rappaport, Lukes-Collins, Working Formulation, and Kiel criteria. Twenty-one (58%) of the 36 patients had lymphomas classified as lymphoplasmacytic/lymphoplasmacytoid type or LP immunocytoma (LPI) according to the Kiel classification. The remainder of the patients (42%) had lymphomas distributed among the follicular center cell (FCC) types and immunoblastic sarcoma in the Lukes-Collins classification. Survival of patients with LPI was significantly longer than that of patients with other types of lymphoma (88% versus 47% 5-year actuarial survival estimate), and the LPIs were more often confined to the lung without hilar or mediastinal lymph node involvement. Seven (33%) of the 21 LPI eventually recurred after a mean follow-up of 69 months, and 4 of these 7 developed serum paraproteins. Most of the patients with lymphomas other than LPI had persistent disease or an early recurrence. LPI, as described by Lennert, seems prone to arise in extranodal sites and to recur late. Measurement of serum immunoglobulins may be helpful in detecting recurrences of LPI.