This study aimed at determining the prevalence of INK4 deletions and their impact on outcome in 125 children with acute lymphoblastic leukemia (ALL) at first relapse using real-time quantitative polymerase chain reaction. Patients were enrolled into relapse trials ALL-REZ BFM (ALL-Relapse Berlin-Frankfurt-Münster) 90 and 96. The prevalence of p16(INK4a) and p15(INK4b) homozygous deletions was 35% (44 of 125) and 30% (38 of 125), respectively. A highly significant association of both gene deletions was found with the 2 major adverse prognostic factors known for relapsed childhood ALL: T-cell immunophenotype and first remission duration. There was no correlation between INK4 deletions and probability of event-free survival. These findings argue against an independent prognostic role of INK4 deletions in relapsed childhood ALL.