['The purpose of the present study was to examine the expression levels of microRNA-9 (miR-9) in osteosarcoma tissues and normal bone tissues, and investigate the relationships between miR-9 expression, clinicopathological features and the prognosis of patients with osteosarcoma.', 'The expression levels of miR-9 in osteosarcoma tissues and corresponding non-cancerous tissues were detected using a real-time quantitative assay. Differences in patient survival were determined using the Kaplan-Meier method and a log-rank test. A Cox proportional hazards regression analysis was used for univariate and multivariate analyses of prognostic values.', 'Compared to non-cancerous bone tissues, the expression levels of miR-9 in osteosarcoma tissues were significantly elevated (P\u2009<\u20090.001). We found that the expression level of miR-9 was significantly associated with tumor size (P\u2009=\u20090.011), clinical stage (P\u2009=\u20090.009) and distant metastasis (P\u2009<\u20090.001). The Kaplan-Meier curve showed that patients with low miR-9 expression survived significantly longer than patients with high miR-9 expression (P\u2009=\u20090.0017). Multivariate analysis suggested that miR-9 expression level (P\u2009=\u20090.002) is an independent prognostic factors for overall survival.'] Is microRNA-9 expression a prognostic biomarker in patients with osteosarcoma?