In the present study, we address the issue of the discontinuation of imatinib mesylate (Gleevec) in chronic myelogenous leukemia with undetectable residual disease for more than 2 years. Twelve patients were included. The median duration of real-time quantitative–polymerase chain reaction (RTQ-PCR) negativity and imatinib therapy were, respectively, 32 months (range, 24-46 months) and 45 months (range, 32-56 months) before imatinib interruption. Six patients displayed a molecular relapse with a detectable BCR-ABL transcript at 1, 1, 2, 3, 4, and 5 months. Imatinib was then reintroduced and led to a novel molecular response in most patients. Six other patients (50%) still have an undetectable level of BCR-ABL transcript after a median follow-up of 18 months (range, 9-24 months). We hypothesize that relapses observed within 6 months reflect the kinetics of undetectable dividing chronic myelogenous leukemia (CML) cells. Those cells may be eradicated or controlled in long-term nonrelapsing patients, as described in our study.