Emergency department (ED) patients with acute pulmonary embolism (PE) may undergo diagnostic pulmonary imaging as an outpatient before referral to the ED for definitive management. This population has not been well characterized. This retrospective cohort study included ambulatory adults with acute objectively confirmed PE across 21 EDs in an integrated health care system from January 1, 2013, through April 30, 2015. We excluded patients arriving by ambulance. We compared outpatients with diagnostic pulmonary imaging in the 12 hours prior to ED arrival (the clinic-based cohort) with those receiving imaging for PE only after ED arrival. We reported adjusted odds ratio (aOR) with 95% confidence intervals (CIs) for hospitalization, adjusted for race, presyncope or syncope, proximal clot location, and PE Severity Index class. Among 2,352 eligible ED patients with acute PE, 344 (14.6%) had a clinic-based diagnosis. This cohort had lower PE Severity Index classification and were less likely to be hospitalized than their counterparts with an ED-based diagnosis: 80.8% vs. 92.0% (p < 0.0001). The inverse association with hospitalization persisted after adjusting for the above patient characteristics with aOR of 0.36 (95% CI = 0.26 to 0.50). In the study setting, ambulatory outpatients with acute PE are commonly diagnosed before ED arrival. A clinic-based diagnosis of PE identifies ED patients less likely to be hospitalized. Research is needed to identify which patients with a clinic-based PE diagnosis may not require transfer to the ED before home discharge.