Human telomerase reverse transcriptase (hTERT) is the catalytic component of telomerase enzyme and has been shown to be associated with telomerase activity (TA). Although many studies in adult leukemia have established the importance of TA, very few have been reported in the children. In this study hTERT levels in childhood leukemia was evaluated and compared with the prognostic factors described before. The LightCycler instrument was used (online real-time PCR) for the quanti. cation of hTERT in peripheral blood and bone marrow in 23 cases with acute lymphoblastic leukemia (ALL) and in 8 cases with acute myeloblastic leukemia (AML). Ten cases with normal peripheral blood (PB) and bone marrow (BM) were selected as control group. Cytogenetic analyses were available in 21 patients with leukemia. In all cases with acute leukemia and in control group, peripheral blood (PB) hTERT levels correlated significantly with bone marrow (BM) hTERT levels. Before treatment, patients with ALL had significantly higher hTERT levels than that of AML patients and control cases. Among patients with ALL, higher hTERT levels were observed in patients with pre-B leukemia, followed by B cell and T cell leukemia patients. Initially increased hTERT levels decreased to the nearly normal levels during remission in cases with ALL. No correlation was observed between the initial hTERT levels and the known prognostic factors except cytogenetic findings. Higher hTERT levels were detected in patients having karyotypic abnormalities which indicate poor prognosis. hTERT levels are significantly high in childhood ALL with the highest level of pre-B cell leukemia before treatment. Those high levels of hTERT decrease to almost normal levels in remission. hTERT levels might be useful in monitoring of leukemia in children.