BACKGROUND The aim of this study was to measure and compare the plasma levels of the microRNA (miRNA), miR-221, in patients with acute pulmonary embolism (PE) with healthy individuals and to evaluate the potential role of miR-221 as a diagnostic biomarker for acute PE. MATERIAL AND METHODS In blood samples collected from 60 patients with acute PE and 50 healthy volunteers, plasma levels of microRNA were identified using a microRNA microarray, and miR-221 expression was detected using real-time quantitative reverse transcription polymerase chain reaction (qRT-PCR). Brain natriuretic peptide (BNP) and troponin I were measured using an automated immunoassay analyzer. D-dimer levels were measured with an enzyme-linked immunosorbent assay (ELISA). RESULTS From the evaluation of 32 differentially expressed plasma miRNAs, miR-221 was significantly upregulated in the plasma of patients with acute PE compared with normal individuals (P<0.05). Correlation analysis showed that plasma miR-221 levels in patients with acute PE were positively correlated with levels of BNP (r=0.842, P<0.05), troponin I (r=0.853; P<0.05), and D-dimer (r=0.838; P<0.05). The receiver operating characteristic (ROC) area under the curve (AUC) for plasma miR-221 was 0.823 (95% CI, 0.757-0.906) (P<0.05), compared with the AUC for D-dimer of 0.768 (95% CI, 0.727-0.853), the AUC for troponin I of 0.713 (95% CI, 0.646-0.868), and the AUC for BNP of 0.648 (95% CI, 0.601-0.723). CONCLUSIONS Plasma levels of miR-221 were significantly increased in patients with acute PE when compared with healthy individuals.