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Aim. To assess the efficacy of FLAG/FLAG-Ida regimen and to identify factors that influence remission, duration of disease-free survival (DFS) and overall survival (OS) of patients with relapsed/refractory acute myeloid leukemia (AML). Materials & Methods. The trial included 54 patients (28 men and 26 women), median age was 37 years (range 18-70 years). 27 (50 %) out of 54 patients had refractory AML and 27 (50 %) patients had relapsed AML. FLAG and FLAG-Ida regimens were administered as induction therapy. 37 (68.5 %) patients received bone marrow transplantation. Molecular genetic and cytogenetic examinations were performed prior to therapy and on the 28th day after the start of treatment. WT1 gene expression was evaluated on the 14th-16th day of treatment. Results. Complete remission (CR) was achieved in 42 (77.8 %) out of 54 patients. Refractoriness to therapy was observed in 9 (16.7 %) out of 54 patients, mortality was 5.5 % (3/54). Remission rate was higher in patients with relapsed AML compared with refractory AML: 85.2 % (23/27) and 70.4 % (19/27), respectively. On the 14th-16th day of treatment patients with blast cell count ≥ 10 % in bone marrow (BM) showed significantly lower CR rate (60 %) compared with the group of patients with < 10 % blast cells in BM (89.6 %; p = 0.024) and shorter DFS (median 7.6 vs. 17.6 months, respectively; p = 0.03). Median DFS in patients with WT1 expression reduction to < 1 log on the 14th-16th day was 5 vs. 18 months in patients without WT1 expression reduction (p = 0.01). DFS varied in groups of patients with blast cell count < 10 % in BM on the 14th-16th day of treatment based on the level of WT1 expression reduction (p = 0.04). MRD-negative patients (57.1 %) showed significantly longer DFS and OS compared with MRD-positive patients (median DFS was 17.6 vs. 5.2 months, respectively, p = 0.02; median OS was 19 vs. 6.9 months, p = 0.0002). Median DFS and OS were different only in ELN low- and high-risk groups (median not reached vs. 5.2 months, respectively, p = 0.039; median not reached vs. 10.2 months, p = 0.039). Conclusion. FLAG and FLAG-Ida are effective and safe regimens in the treatment of relapsed/refractory AML. Achieving remission depends on neither the risk group nor the time of relapse occurrence. The blast cell count in BM on the 14th-16th day of FLAG/FLAG-Ida treatment is a prognostic factor determining achievement and duration of remission. WT1 expression level in the early post-induction period is a sensitive DFS marker. MRD status and molecular genetic risk (ELN) group affiliation are essential prognostic factors determining DFS and OS.