OBJECTIVE To evaluate the prevalence of FLT3 gene expression and internal tandem duplication (ITD) mutation in acute myeloid leukemia (AML) patients and its clinical significance. METHODS The expression level of FLT3 mRNA was detected with real-time quantitative RT-PCR (RQ-PCR) technique in 152 bone marrow samples from 129 AML patients. The ITD of the FLT3 gene (FLT3/ITD) was detected in 75 de novo AML patients by reverse transcription polymerase chain reaction (RT-PCR). RESULTS The expression levels of FLT3 mRNA was 0.0020(0.0006 - 0.0040) in normal controls, and 0.1041 (0 - 33.8736) in 80 de novo AML patients (P = 0.001). FLT3/ITDs were found in 11 (14.7%) of 75 de novo AML patients. The FLT3 expression levels in patients with FLT3/ITD were 0.0297 to 33.8736 with a median level of 0.2200, and in those without FLT3/ITD were 0 to 26.2200 with a median level of 0.0975. The FLT3 expression levels in the former patients were higher than that in the latter ones, but there was no statistical significance (P = 0.093). The complete remission (CR) rate was lower in acute promyelocytic leukemia (APL) patients with FLT3/ITD than in APL patients without FLT3/ITD (P = 0.015). In de novo AML other than APL patients without FLT3/ITD, the CR rate was lower in patients with higher levels of FLT3 expression (expression level > 0.04, CR rate 37.5%) than those with lower levels of FLT3 expression (expression level < 0.04, CR rate 100%). On follow-up of 20 patients, the FLT3 expression level was decreased at least one logarithm degree when they got CR, but it was no significant change in non-remission patients. CONCLUSIONS Quantification of FLT3 mRNA expression level and detection of FLT3/ITD in AML patients may serve as an index for evaluating therapeutic efficacy, predicting prognosis, and monitoring minimal residual disease.