PURPOSE: The prognostic factors in acute lymphoblastic leukemia was patient's age at diagnosis, sex, hepatosplenomegaly, initial WBC & platelet count. Recently immunophenotype has being studied as guidance for several treatment protocol. We performed a retrospective study to evaluate the significance of immunophenotype on clinical course & long-term survival in children with acute lymphoblastic leukemia. METHODS: One hundred two children with acute lymphoblastic leukemia were admitted to the Department of Pediatrics, Yonsei University College of Medicine from Jan.1991 to Dec. 1995, and bone marrow aspiration biopsies and immunophenotyping were performed. The prognostic significance of immunophenotype was evaluated base on the median event free survival and probability of survival at the end of follow-up. RESULTS: 1) In 102 children comprised 14 cases under 2 years old, 71 cases from 2 to 10 years of age and 17 cases above 10 year old. The ratio of male to female was 6 : 4. 2) By CCG risk grouping, standard risk in 21 cases, intermediate risk in 35 cases, high risk in 46 cases. 3) By cytologic classification of FAB, Ll in 65 cases, L2 in 31 cases, L3 in 2 cases 4) Remission induction rate in early pre-B ALL was 100% (39/39), among those recurrence rate 20% (8/39). 5) Remission induction rate in pre-B ALL was 90% (26/29), among those recurrence rate 54% (14/26). 6) Remission induction rate in B-cell ALL was 33%(113), and all cases was expired during follow-up. 7) Remission induction rate in T-cell ALL was 100% (12/12)), among those recurrence rate 41% (5/12). 8) Remission induction rate in T-B mixed ALL was 71%(517), among those recurrence rate 0% (0/5), but non-remission cases was expired during follow-up. 9) Remission induction rate in Myeloid Ag(+) ALL was 83%(516), among those recurrence rate 80% (415). CONCLUSIONS: These results suggest that better result on long-term survival was observed in early pre-B ALL than in T-cell, 7-B mixed, or Myeloid antigen positive ALL and immunophenotype have prognostic impact in acute Iymphoblastic leukemia.