Aim To assess the expression level of fms-like tyrosine kinase 3 (FLT3), the incidence of FLT3/internal tandem duplications (ITD) mutation, and prognostic value of FLT3 changes in different types of adult leukemia. Methods Bone marrow mononuclear cells were isolated from 147 adult patients with leukemia. Reverse transcriptase polymerase chain reaction (PCR) was used to screen FLT3/ITD mutation and quantitative PCR was performed to evaluate the expression of the FLT3 transcript. Flow cytometry was used for detection of FLT3 receptor protein expression on bone marrow mononuclear cells. Pearson correlation analysis was performed to estimate the significance of FLT3. Results FLT3 expression was higher in acute myeloid leukemia and Bacute lymphoid leukemia than in T-acute lymphoid leukemia (P = 0.006, P = 0.001) and chronic myelogenous leukemia (P < 0.001). In chronic myelogenous leukemia, FLT3 expression in blast transformation phase was higher than in acceleration phase (P = 0.023). Surface expression of FLT3 protein was correlated with high percentage of bone marrow blasts and with FLT3 mRNA expression (r = 0.366, P < 0.001) in acute leukemia. FLT3/ITDs in the juxtamembrane domain were found in 25% of patients with acute myeloid leukemia and 7% of patients with acute lymphoid leukemia. FLT3/ITD positive sequences had 36, 42, and 57 nucleotides. FLT3/ITD mutation was associated with a higher white blood cell count, higher marrow blast percentage, and elevated serum lactate dehydrogenase (P = 0.045, P = 0.014, P < 0.001, respectively) and not associated with a higher FLT3 mRNA and FLT3 protein expression, and lower complete remission (P = 0.091, P = 0.060, P = 0.270, respectively). Conclusion FLT3 expression levels differed in different types of adult leukemia. Overexpression of FLT3 and presence of a positive FLT3/ ITD mutation in acute leukemia were associated with unfavorable clinical characteristics and poor prognosis.