Substantial progress has been made in the treatment of precursor B-cell acute lymphoblastic leukemia (B-ALL), but recurrent disease remains a leading cause of death in children due to cancer and outcomes for adults with B-ALL remain poor. Recently, complete clinical responses have been observed in small numbers of patients with B-ALL treated with adoptive immunotherapy using T cells genetically engineered to express chimeric antigen receptors (CARs) targeting CD19, a cell surface molecule present in essentially all cases of B-ALL. Preclinical data suggest that CARs targeting CD22, another antigen present in the majority of B-ALL cases, are similarly potent. Several clinical studies already under way will soon more clearly define the rate of response to this novel therapy in B-ALL. Further work is needed to identify optimal platforms for CAR-based adoptive immunotherapy for leukemia, to establish guidelines for managing toxicity, and to determine whether the remissions induced by this approach can be rendered durable.