A most important set of prognostic factors for survival among 467 patients with non-Hodgkin's lymphoma receiving conservative treatment was determined statistically by the Cox proportional hazards model. Non-Hodgkin's lymphoma was diagnosed in these patients between 1958 and 1969. Initial biopsy material was classified according to the Working Formulation, and the Rappaport, Kiel, and Lukes-Collins systems. The Cox analysis identified a group of 37 patients with a median survival of 150 months. These patients had the following characteristics: small lymphocyte, plasmacytoid lymphocyte, small cleaved, large cleaved or non-cleaved follicular center cell histologic subtype (Lukes-Collins); no bulky involvement of mesenteric nodes or critical organs--kidney, urinary tract, or pleura; stages I to III disease (78 percent stage I or IE); no B symptoms; age below 60 years; initial resection as a reflection of localized disease. Patients with advanced-stage non-Hodgkin's lymphoma receiving conservative treatment have a relatively short survival (median, less than five years) regardless of histologic subtype.