Seven Philadelphia chromosome-positive acute lymphoblastic leukemia (Ph+ALL) patients in first complete remission received maintenance therapy with imatinib alone. Two-year progression-free survival was 75%. Quantitative polymerase-chain-reaction (qPCR) monitoring of BCR-ABL showed that: (i) persisting molecular complete response (CR) was associated with long-lasting CR; (ii) molecular relapse did not invariably mean hematologic relapse; (iii) only the wide and rapid increment of BCR-ABL values was predictive of leukemia relapse.