Background: The pulmonary artery obstruction index (PAOI), which is evaluated by the CT pulmonary angiography, offers an objective method to measure the severity of pulmonary arteries obstruction. Objectives: We decided to investigate the correlation between the PAOI determined by CT pulmonary angiography, as an index to determine the severity of pulmonary embolism (PE), with two clinical models used for predicting the probability of acute PE, namely the Wells criteria and the simplified revised Geneva score. Patients and Methods: Sixty-four consecutive patients with definite diagnosis of acute PE based on CT pulmonary angiography were enrolled. The Wells score as well as simplified revised Geneva score were calculated retrospectively using the medical records. Then, the PAOI was determined by CT pulmonary angiography. By applying the Pearson's correlation coefficient, the relationships were investigated. Results: The Wells score had a weak correlation with the PAOI (r = 0.29; P = 0.01). The simplified revised Geneva score did not have significant correlation with the PAOI (r = 0.1; P = 0.2). Furthermore, patients with active cancer had significantly higher CT indexes than the other patients with PE (P = 0.046). Conclusion: Although the Wells and simplified revised Geneva scores are used widely for assessing clinical probability of PE, these scores may not necessarily correlate with the severity of PE. The Wells score had a weak correlation and may somehow predict the severity of PE. Malignancy is a significant risk factor found to be correlated with more severe PE.