In The Netherlands from July 1988 to October 1991, children (0 to 16 years of age) with de novo acute lymphoblastic leukemia (ALL) were treated according to protocol ALL-7 of the Dutch Childhood Leukemia Study Group (DCLSG). In this protocol, chemotherapy and treatment stratification were identical to the ALL-BFM-86 protocol (Reiter et al, Blood 84:3122, 1994), but cranial irradiation was restricted to patients with initial central nervous system (CNS) involvement. Patients were stratified into 3 risk groups, based on leukemia cell mass and response to initial treatment: standard-risk group (SRG), risk group (RG), and experimental group (EG). As in ALL-BFM-86, a randomized study on late intensification (protocol S) was performed in RG patients, and during the study (since October 1990), early reinduction treatment (protocol II) was introduced for SRG patients. Treatment duration for all patients was 18 months. Two hundred eighteen children entered the study: 74 SRG, 127 RG, and 17 EG patients. The overall complete remission (CR) rate was 98%. The 5-year event-free survival (EFS) for all DCLSG ALL-7 patients was 65.3% (standard error [SE] 3.2%), which was significantly different from the 73% (SE 1%) 5-year EFS achieved in the ALL-BFM-86 study (P = .02, Z-test). However, restricting the analysis to SRG patients receiving protocol II with a total duration of treatment of 18 months, the 5-year EFS rates were 64.6% (SE 4.0%) and 67% (SE 4%), respectively, and no significant difference could be established (P = .67, Z-test). The 5-year EFS rates for SRG, RG, and EG patients were 63.5% (SE 5.6%), 66.6% (SE 4.2%), and 63.3% (SE 12.0%), respectively. SRG patients receiving protocol II fared better than patients not receiving protocol II (5-year EFS 76.7% [SE 7.7] and 54.5% [SE 7.5], respectively). No difference in 5-year EFS was observed in RG patients randomized to receive or not to receive late intensification with protocol S. The overall CNS relapse rate at 5 years was 5.5%. The incidence rate at 5 years was 11.4% in SRG patients not receiving protocol II, whereas no CNS relapses occurred in SRG patients receiving protocol II. Six children died in first complete remission and 2 children developed a second malignancy (thyroid carcinoma and acute nonlymphoblastic leukemia). Systemic high-dose methotrexate (MTX) and intrathecal chemotherapy is a safe and effective method of CNS prophylaxis in the context of BFM-oriented treatment for all children with ALL, regardless of the risk group (with the possible exception of T-ALL patients with high white blood cell counts). The results of the DCLSG ALL-7 study confirm those of the ALL-BFM-86 study showing that early reinduction with protocol II is essential in the treatment of SRG patients and that late intensification with protocol S does not improve the prognosis for RG patients.