We reported the treatment outcome of Protocol 8704T, which included repeated L-asparaginase, for childhood T cell malignancies. Fifteen cases of acute lymphoblastic leukemia (T-ALL) and 11 cases of non-Hodgkin's lymphoma (T-NHL), aged 3 to 14 yrs (median 6 yrs), were enrolled. Twelve T-ALL had mediastinal mass. Murphy's stages of T-NHL were 6 with III and 5 with IV. Types of histology consisted of 8 lymphoblastic and 3 large cell. Treatment was performed for 2 years. Observation periods were from 14 months to 78 months (median 42 months). Twenty-three achieved remission and 6 of them were transplanted with bone marrow or peripheral stem cells in the first remission. The protocol was continued in 17 cases. Fourteen of them remain in first remission, but one died of measles and 2 died of relapse. The 5-year event-free survival was 76.1% for ALL and 65.5% for NHL. In terms of histology, it was 87.5% for lymphoblastic NHL and 33.3% for large cell NHL (p = 0.19). In terms of phenotypes in ALL, it was 88.7% for ALL positive to CD2, 5 and 7, while 2 ALL positive to CD7 alone both failed. Therefore, it was shown that this treatment protocol is very effective for T-lymphoblastic leukemia and lymphoma.