Introduction: Diagnosing pulmonary embolism (PE) can be challenging because the signs and symptoms are often non-specific. Studies have shown that evidence-based algorithms are not always adhered to in the Emergency Department (ED), which leads to unnecessary CT scanning. The pulmonary embolism rule-out criteria (PERC) can identify patients who can be safely discharged from the ED without further investigation for PE. The purpose of this study is to evaluate the use of the PERC rule in the ED and to compare the rates of testing for PE if the PERC rule was used. Methods: This was a health records review of ED patients investigated for PE at two emergency departments over a two-year period (April 2013-March 2015). Inclusion criteria were ED physician ordered CT pulmonary angiogram, ventilation-perfusion scan, or D-dimer for investigation of PE. Patients under the age of 18 were excluded. PE was considered to be present during the emergency department visit if PE was diagnosed on CT or VQ (subsegmental level or above), or if the patient was subsequently found to have PE or deep vein thrombosis during the next 30 days. Trained researchers extracted anonymized data. The rate of CT/VQ imaging and the negative predictive value was calculated. Results: There were 1,163 patients that were tested for PE and 1,097 patients were eligible for our analysis. Of the total, 330/1,097 (30.1%; 95%CI 27.4-32.3%) had CT/VQ imaging for PE, and 48/1,097 (4.4%; 95%CI 3.3-5.8%) patients were diagnosed with PE. 806/1,097 (73.5%; 95%CI 70.8-76.0%) were PERC positive, and of these, 44 patients had a PE (5.5%; 95%CI 4.1-7.3%). Conversely, 291/1,097 (26.5%; 95%CI 24.0-29.2%) patients were PERC negative, and of these, 4 patients had a PE (1.4%; 95%CI 0.5-3.5%). Of the PERC negative patients, 291/291 (100.0%; 95%CI 98.7-100.0%) had a D-dimer test done, and 33/291 (11.3%; 95%CI 8.2-15.5%) had a CT angiogram. If PERC was used, CT/VQ imaging would have been avoided in 33/1,097 (3%; 95%CI 2.2-4.2%) patients and the D-dimer would have been avoided in 291/1,097 (26.5%; 95%CI 24.0-29.2%) patients. Conclusion: If the PERC rule was used in all patients with suspected PE, fewer patients would have further testing. The false negative rate for the PERC rule was low.