Summary Background Short intensive chemotherapy is the standard of care for adult patients with Burkitt's leukaemia or lymphoma. Findings from single-arm studies suggest that addition of rituximab to these regimens could improve patient outcomes. Our objective was to test this possibility in a randomised trial. Methods In this randomised, controlled, open-label, phase 3 trial, we recruited patients older than 18 years with untreated HIV-negative Burkitt's lymphoma (including Burkitt's leukaemia) from 45 haematological centres in France. Exclusion criteria were contraindications to any drug included in the chemotherapy regimens, any serious comorbidity, poor renal (creatinine concentration >150 μmol/L) or hepatic (cirrhosis or previous hepatitis B or C) function, pregnancy, and any history of cancer except for non-melanoma skin tumours or stage 0 (in situ) cervical carcinoma. Patients were stratified into two groups based on disease extension (absence group B or presence group C of bone marrow or central nervous system involvement). Patients were further stratified in group C according to age (<40 years, 40–60 years, and >60 years) and central nervous system involvement. Participants were randomly assigned in each group to either intravenous rituximab injections and chemotherapy (lymphome malin B LMB) or chemotherapy alone by the Groupe d'Etude des Lymphomes de l'Adulte datacentre. Randomisation was stratified by treatment group and centre using computer-assisted permuted-block randomisation (block size of four; allocation ratio 1:1). We gave rituximab (375 mg/m2 ) on day 1 and day 6 during the first two courses of chemotherapy (total of four infusions). The primary endpoint is 3 year event-free survival (EFS). We analysed all patients who had data available according to their originally assigned group. This trial is registered with ClinicalTrials.gov , number NCT00180882. Results Between Oct 14, 2004, and Sept 7, 2010, we randomly allocated 260 patients to rituximab or no rituximab (group B 124 patients 64 no rituximab; 60 rituximab; group C 136 patients 66 no rituximab; 70 rituximab). With a median follow-up of 38 months (IQR 24–59), patients in the rituximab group achieved better 3 year EFS (75% 95% CI 66–82) than did those in the no rituximab group (62% 53–70; log-rank p stratified by treatment group=0·024). The hazard ratio estimated with a Cox model stratified by treatment group, assuming proportionality, was 0·59 for EFS (95% CI 0·38–0·94; p=0·025). Adverse events did not differ between the two treatment groups. The most common adverse events were infectious (grade 3–4 in 137 17% treatment cycles in the rituximab group vs 115 15% in the no rituximab group) and haematological (mean duration of grade 4 neutropenia of 3·31 days per cycle 95% CI 3·01–3·61 vs 3·38 days per cycle 3·05–3·70) events. Interpretation Addition of rituximab to a short intensive chemotherapy programme improves EFS in adults with Burkitt's leukaemia or lymphoma. Funding Gustave Roussy Cancer Campus, Roche, Chugai, Sanofi.