We investigate the potential role of candidate polymorphisms in SLCO1B1 (rs4149056 and rs2306283), ABCB1 (rs1045642), ABCC2 (rs717620), ABCC3 (rs9895420), and ABCC4 (rs7317112) drug transporters genes on HD‐MTX pharmacokinetics and patients' outcome (meant both as relapse and drug‐related toxicities) in an Italian cohort of 204 ALL pediatric patients treated according to the AIEOP‐BFM ALL 2009 protocol. Here, ABCC4 is linked to acute lymphoblastic leukemia.