Thirteen adult patients with histologically confirmed lymphoblastic lymphoma were treated with an intensive chemotherapy program consisting of induction with cyclophosphamide, adriamycin, vincristine, and prednisone (modified CHOP); consolidation and central nervous system (CNS) prophylaxis with methotrexate intrathecally and by high-dose intravenous injection, citrovorum factor and L-asparaginase; reinforcement with CHOP; and maintenance with 6-mercaptopurine and methotrexate. Treatment duration was 1 yr. A 14th patient with T-cell acute lymphoblastic leukemia was also treated at presentation by the same regimen. Thirteen patients had at least a mediastinal mass or abnormal cells in the bone marrow; one presented with CNS disease. The median age was 22 yr (range 16--50), and male--female ratio was 2.5:1. All patients had a rapid complete clinical response. Of the 13 patients without initial CNS disease, 4 have relapsed, 3 with primary CNS relapse and 1 with a recurrent abdominal mass. Five patients have died, 2 from drug toxicity, 2 from CNS relapse, and 1 from chronic myelogenous leukemia, which was diagnosed simultaneously with the lymphoblastic lymphoma. The median follow-up is 19 mo, and all patients have completed their planned therapy. At 3 yr, the actuarial survival is 61% and relapse-free survival is 56%.