Despite intensified chemotherapy, adolescents with acute lymphoblastic leukemia (ALL) still have lower rates of survival than younger children. The purpose of our study was to compare the treatment outcome and presenting clinical and laboratory features of adolescent and younger children with newly diagnosed ALL who were treated at our pediatric hematology department. Between April 1991 and February 2000, 42 children up to 18 years of age who were newly diagnosed with ALL and treated adequately with modified ALL Berlin-Frankfurt-Münster (BFM) 90 or 95 protocols were included in this study. The patients were examined in two groups according to their ages: the first group consisted of children who were <14 years old and the second group consisted of adolescents who were >14 years old. The median age of 42 patients was 6.5 years (range: 1-16.5 years); 26% of the patients were adolescents. The results of this study demonstrated that after a median observation time of 6 years the overall survival (OS) and event-free survival (EFS) of patients who were <14 and >14 years of age were 75% vs 49% and 70% vs 40%, respectively. When adolescent and younger patients were compared to each other according to gender, WBC count at administration, French-American-British (FAB) classification, immunophenotypes, risk groups, early deaths, and relapse rates, there were no statistically significant differences. Comparative data from other studies and data from this study indicate that adolescents with ALL still have shorter OS and EFS than younger children and a steady improvement in treatment outcome for adolescents with ALL over time suggests that more intensive therapy favorably influences prognosis.