The polymorphism of 14-bp tandem repeat sequence located in the ASNS gene probably acts as a transcriptional enhancer element and leads to higher expression of the gene in carriers of more than 2 repeats (>R2). We searched for an association with disease outcome in 264 children with ALL. A multivariate proportional hazard regression model adjusted for age at diagnosis (HR (95%CI)=1.05 (1.04-1.09)) and high-risk group (HR(95%CI)=3.47 (1.74-6.88)) revealed that R3 carriers with a poor response at day 15 had an increased risk of events, HR (95%CI)=2.72 (1.06-6.96). These results suggest a conditional interaction between the ASNS polymorphism and an early response to chemotherapy among pediatric patients with ALL.