Objectives: The objective was to assess and compare the accuracy and interobserver reliability of the simplified Pulmonary Embolism Severity Index (sPESI) and the Hestia criteria for predicting short-term mortality in patients with pulmonary embolism (PE). Methods: This prospective cohort study evaluated consecutive eligible adults with PE diagnosed in the emergency department (ED) at a large, tertiary, academic medical center in the era January 1, 2015, to December 30, 2017. We assessed and compared sPESI and Hestia criteria prognostic accuracy for 30-day all-cause mortality after PE diagnosis and their interobserver reliability for classifying patients as low risk or high risk. Two clinician investigators scored both prediction tools during the ED evaluation. We used the kappa statistic to test for agreement. Results: The 488-patient cohort had a mean (±SD) age of 69.0 (±17.1) years and an approximately even sex distribution. The investigators classified one-quarter of patients as low risk using the sPESI and Hestia criteria (28% vs. 27%, respectively). During the 30-day follow-up, 31 of the 488 (6.4%) patients died. Patients classified as low risk according to the sPESI and the Hestia criteria had a similar 30-day mortality (sPESI 0.7% [1/135], 95% confidence interval [CI] = 0.0%–4.0%; Hestia 2.3% [3/132], 95% CI = 0.5%–6.5%). The two observers had good agreement (κ = 0.80) for the Hestia criteria and very good agreement (κ = 0.97) for the sPESI. Conclusion: The sPESI and the Hestia criteria had similar risk classification determination and prognostic accuracy for 30-day mortality after PE. However, the succinct and more objective sPESI had higher interobserver reliability than the Hestia criteria.