OBJECTIVES: Rituximab (MabThera) combined with CHOP chemotherapy (R-CHOP) significantly prolongs event-free and overall survival of patients with diffuse large B-cell lymphoma (DLCL) (GELA LNH 98-5 Study). We estimated the cost-effectiveness of R-CHOP. METHODS: The analyses were based on a randomized-controlled trial comparing R-CHOP with CHOP, from a French health system perspective. Patients (n=399) were eligible if age 60-80 years, had stage II-IV DLCL, and had ECOG performance status of 0-2. Mean patient survival in each treatment arm and chemotherapy costs during treatment (q3 weeks x 8 cycles) were estimated from trial data. The longest duration of follow-up was 34 months. We estimated survival and cost-effectiveness up to a time horizon of 10 years. Survival for each IPI strata was estimated using the Kaplan-Meier method; survival after the longest observed time in the trial was estimated using published mortality rates (Shipp, NEJM, 93). French DRG payments were applied to trial data on hospital use and treatments for adverse events. French drug prices and drug administration costs were used to estimate the costs of R-CHOP and CHOP regimens. Costs and survival were discounted at 3.0%. R-CHOP increased survival from 56% to 63% at the time of last follow-up (34 months). RESULTS: The mean duration of survival was 820 days for R-CHOP and 721 days for CHOP, resulting in a mean increase in survival of 0.27 years. Extrapolating to 10 years, R-CHOP is projected to increase discounted mean survival by 0.54 years. Therapy-related cost during the trial period was 15,000 euros higher with R-CHOP, with a cost per life-year gained (LYG) of 55,300 euros. Over 10 years, total added cost per patient was 15,270 euros and the estimated cost per LYG was 28,410 euros. CONCLUSIONS: R-CHOP increases chance of cure compared with CHOP and is cost-effective compared with other treatments in widespread use.