Background: Acute lymphoblastic leukemia (ALL) is the most prevalent cancer in the pediatric population. From 25% to 30% of patients with ALL will have a relapse that leads to death when they are teenagers. At Cipto Mangunkusumo Hospital, 40% of 126 pediatric patients with ALL relapsed from 2005 to 2011. A multiple variant of multidrug resistance gene 1 (MDR1) is C3435T, which can be used to understand the genetic basis of susceptibility to relapse. Objectives: To identify the profile of MDR1 polymorphism in pediatric Indonesian patients with ALL. Methods: We collected data from 44 patients with ALL who attended Cipto Mangunkusumo Hospital between January and June 2014. We investigated a silent C3435T polymorphism in MDR1 exon 26 with polymerase chain reaction-restriction fragment length polymorphism using MboI. Results: There were 32 male and 12 female patient participants in this study. Eighteen patients were 1−3 years old and 26 were over 3 years. The mean age at 1−3 years was 2.4 ± 0.86, and over 3 years it was 6.3 ± 2.67 years. There were 27 patients with ALL in the standard risk group and 17 in the high risk group. We determined that the 25 samples from patients with ALL in the standard risk group were not digestible (allele T) and the 6 samples from patients with ALL in the high risk group were digestible (allele C). Conclusions: The prevalence of the T allele was higher than that of the C allele in pediatric Indonesian patients with ALL.