The feasibility and efficacy of cyclophosphamide, vincristine, doxorubicin, and methotrexate (CODOX-M)/ifosfamide, etoposide, and cytarabine (IVAC) therapy in Japanese adult patients with Burkitt lymphoma (BL) and B cell lymphoma, unclassifiable, with features intermediate between diffuse large B cell lymphoma and BL (intermediate DLBCL/BL) have never been reported. The effects of adding rituximab to CODOX-M/IVAC have not been published either. Fifteen consecutive patients with a median age of 39 years were treated with modified CODOX-M/IVAC regimen (particularly, reducing the dose of methotrexate to 3 g/m(2)) with or without rituximab at our institution. Although all patients developed grade 4 neutropenia and grade 3/4 thrombocytopenia/anemia, 93% had febrile neutropenia, 60% showed transaminase elevation, and 40% had mucositis/stomatitis (all grade 3), there were no treatment-related deaths. Two of nine patients treated with rituximab developed biphasic late-onset neutropenia. Thirteen patients (87%) showed complete responses. The remaining two patients had refractory disease; one had presented with peritoneal dissemination and complex chromosomal abnormalities, while the other had double IGH-MYC and IGH-BCL2 translocations. The estimated 5-year overall and progression-free survival were 87% each, with a median follow-up of 74 months. In conclusion, our modified CODOX-M/IVAC regimen is well tolerated and highly effective in Japanese adult patients with BL and intermediate DLBCL/BL, warranting a larger study for confirmation.