Older patients with Burkitt lymphoma/leukemia (BL) have inferior outcomes. Because cyclophosphamide is highly active in BL and can be dose-escalated without stem-cell rescue, we designed a short, cyclophosphamide-intensive regimen without anthracyclines for patients aged ≥30 with untreated, non-HIV-associated BL/atypical BL. Two cycles involving cyclophosphamide 1500 mg/m2, vincristine, rituximab, prednisone, methotrexate 3 g/m2, and intrathecal cytarabine were delivered 2 weeks apart, followed by intensification with high-dose cyclophosphamide (50 mg/kg/day for 4 days) and rituximab. Of 21 patients, median age 53 (range, 34–75), 71% had stage IV, 95% were high-risk and 29% had performance status 3–4. Response occurred in all evaluable patients post-cycle 2 and in 76% post-intensification. Five non-relapse deaths occurred (four before intensification). The estimated 1-year and 3-year event-free survival was 52%; 1-year and 3-year overall survival was 57%. Seventeen (81%) received intensification (median 30 days to intensification). Brief, anthracycline-sparing, intensive cyclophosphamide (BASIC) therapy yields durable remissions in poorer-risk BL/atypical BL.