Purpose: We aimed to evaluate the expression level of programmed death ligand-1 (PD-L1) and its effects on prognosis in acute myeloid leukemia. Methods: The flow cytometry was used to detect PD-L1 expression on leukemic cells of 86 de novo acute myeloid leukemia patients with longitudinal follow-up. Results: Median follow-up was 13 (0-73) months. The mean of expression level was 3.22 +/- 0.47 at diagnosis and ranged from 0 to 28%. PD-L1 expression tended to be lower in patients with acute promyelocytic leukemia (2.47 +/- 1.08, p = 0.09) but there was no significant difference between neither diagnostic nor cytogenetic subgroups. There was no difference in PD-L1 levels between the patients who achieved complete remission (3.4 +/- 0.61) and those who did not (2.91 +/- 0.72, p = 0.94). The patients with low PD-L1 at diagnosis (median 25 mo [95% CI; 0-56.7]) had a longer overall survival compared with high PD-L1 (median 13 mo [95% CI; 5.52-25.17], p = 0.079). PD-L1 expression was lower at relapse (2.04 +/- 0.79) compared to initial diagnosis (4.52 +/- 0.93, p = 0.049). The patients who had overall survival longer than 1 year showed lower PD-L1 expression at relapse (0.66 +/- 0.93) compared with who had not (5.06 +/- 4.28, p = 0.052). A negative correlation between CD33 and PD-L1 (r = - 0.303, p = 0.005) was detected. Conclusion: Despite its low expression levels, PD-L1 appears to be a clinically important prognostic factor. The negative correlation determined between PD-L1 and CD33 supports the combination approach of PD-L1 inhibitors and CD33 targeted immunotherapies.