The objective of this study was to evaluate the advantages of cytomegalovirus (CMV) real-time PCR in blood plasma to monitor CMV infection in a population of adult and pediatric bone marrow recipients in comparison with the pp65 antigenemia method. Fifty allogeneic bone marrow transplant recipients from our center, including 23 adults and 27 children, were enrolled. A CMV real-time PCR designed to amplify a well-conserved region of the UL123 gene was evaluated for its results with whole blood and blood plasma. The CMV real-time PCR assay and the CMV antigenemia method were performed in parallel with 558 blood samples. The results obtained by the two techniques were significantly correlated (r = 0.732; P < 0.0001). Twenty patients developed at least one episode of CMV replication, with a total of 24 episodes detected by CMV PCR; antigenemia assays were positive in 17 of these 24 episodes. The first positive PCR test preceded the first positive antigenemia by a median of 8 days. The median time interval necessary to obtain a negative CMV PCR test after implementation of preemptive treatment was 28 days. CMV PCR of plasma was positive in two children with CMV disease (one with early CMV pneumonia and one with CMV gastroenteritis), while CMV antigenemia remained negative. The use of CMV PCR with plasma to guide both implementation and discontinuation of CMV preemptive therapy might reduce the risk of occurrence of CMV disease since patients would be treated earlier, and it might also help to reduce the duration of treatment, which could attenuate the side effects of antiviral drugs.