Objective: Recently, a novel score for risk stratification of patients with pulmonary embolism (PE)—the HOPPE score—was derived. We aimed to externally validate the HOPPE score in emergency department-diagnosed PE, using SpO2 as a surrogate for PaO2—the modified HOPPE score. Methods: Retrospective observational study of adult patients with an emergency department diagnosis of PE was performed. Data collected included demographics, co-morbidities, clinical features, electrocardiogram and test results, in-hospital mortality and non-fatal major adverse clinical events (MACE; survived cardiac arrest, cardiogenic shock or thrombolysis administration). The primary outcome of interest was clinical performance of the modified HOPPE score for inhospital mortality and the composite outcome of in-hospital death and MACE. A secondary outcome was comparison of predictive performance between the modified HOPPE score and the simplified Pulmonary Embolism Severity Index score. Results: Two hundred and six patients were studied (median age 61, 55% female). There were no deaths or MACE in patients with a low risk modified HOPPE score of 0 to 6 (0%; 95% confidence interval, 0% to 1.8%). Negative predictive value of a low risk score was 100% (95% confidence interval, 92.2% to 100%) for in-hospital mortality and for the composite of in-hospital mortality or MACE. The modified HOPPE score had similar predictive performance to the simplified Pulmonary Embolism Severity Index score with an area under the curve of 0.88 vs. 0.80 for the composite outcome of in-hospital mortality or MACE (P=0.052). Twenty-eight percent of the patients were classified as low risk and potentially suitable for management as outpatients. Conclusion The modified HOPPE score showed good clinical performance. Prospective validation is warranted.