['The aim of this study was to investigate the expression of ubiquitin-specific peptidase 9, X-linked (USP9X) in non-small cell lung cancer (NSCLC) patients and to evaluate the relevance of USP9X expression to tumor prognosis.', 'Ninety-five patients who underwent surgical resection for clinical stage I-IIIA NSCLC between July 2008 and July 2011 were included in this study. Immunohistochemical analysis of USP9X expression was performed on 95 NSCLC tissues and 32 adjacent normal lung parenchymal tissues from these patients. The Chi-squared test was used to compare the clinicopathological characteristics between different groups. Kaplan-Meier analysis and a Cox regression model were used to determine the independent prognostic factors. A P value <0.05 was considered to be significant.', 'The expression of USP9X was found to be significantly higher in NSCLC tissue (44.2%) than in adjacent normal lung parenchymal tissue (6.3%) (P<0.001). High USP9X expression was significantly associated with positive lymph node metastasis (P<0.001), clinical stage (P<0.001) and a reduced overall survival rate (P=0.001) in patients with NSCLC. Based on the multivariate analysis, the elevated expression of the USP9X protein was a significant predictor of poor prognosis for NSCLC patients (HR =2.244, P=0.028).'] Does elevated expression of USP9X correlate with poor prognosis in human non-small cell lung cancer?