Introduction: This study investigates the values of the simplified pulmonary embolism severity index score, its individual criteria, the size of the pulmonary artery in which thrombus was detected by computed tomographic angiography, and systolic pulmonary artery pressure in predicting 30-day, 90 day, and longer-term mortality for patients in two age groups (over and under 65 years of age). Materials and Method: This study evaluated the data of 303 patients. It was designed as a retrospective cohort study and was conducted between January 1, 2019 and March 9, 2019, with a four-year follow up (2011-2015). Results: The mean age of the patients is 57.42 +/- 17.02. Among the patients who died, the simplified pulmonary embolism severity index score was higher than those who survived (p < 0.005), and a correlation was detected between 30-day and 90-day mortality and the score. It was found that pulmonary artery localization with thrombus and pulmonary artery pressure measurement do not have a significant correlation with mortality. While the score is correlated with 30-day and 90-day mortality in the under-65 age group, there was no correlation between 30-day mortality and the score in the over-65 age group. However, 90 day mortality was correlated with the score in the over-65 age group. Conclusion: Although this study validates the score in estimating 30-day and 90-day mortality, it was not sensitive in predicting 30-day mortality in patients over 65 years of age. Moreover, it was not sensitive in the estimation of late mortality after 90 days for this age group.