BACKGROUND The transcription factor Oct-4 is necessary for maintaining pluripotency and self-renewal of embryonic stem cells, and POU5F1B is a processed pseudogene of Oct-4 with coding capacity. The purpose of this study is to evaluate the expression and clinical implication of POU5F1B in AML. MATERIAL AND METHODS The expression of the POU5F1B transcript was evaluated in 175 newly diagnosed AML patients and 39 healthy controls by use of real-time quantitative PCR (RQ-PCR). RESULTS POU5F1B was underexpressed in AML compared with controls (P<0.001). The receiver operating characteristic (ROC) curve revealed that the POU5F1B transcript level was able to differentiate AML patients from healthy individuals (AUC=0.682). In non-APL AML patients, the POU5F1Blow group had significantly higher WBC than the POU5F1Bhigh group (20.2×10⁹ vs. 4.6×10⁹ L⁻¹, P=0.021). Among whole-cohort AML, non-APL AML, and intermediate-risk AML, POU5F1Bhigh patients had obviously higher complete remission (CR) rates than POU5F1Blow patients (P=0.012, P=0.012 and P=0.027). In addition, Kaplan-Meier analysis demonstrated better overall survival (OS, P=0.019, P=0.007 and P=0.046, respectively) in POU5F1Bhigh patients compared with POU5F1Blow patients. Furthermore, in multivariate survival analysis, POU5F1B was independently associated with OS in non-APL AML patients and intermediate-risk AML as a favorable prognostic factor. CONCLUSIONS POU5F1B was frequently underexpressed in AML, and might contribute to the diagnosis and prognosis of AML.