Objectives: This study was conducted to examine the relationship between air pollution and pulmonary embolism in patients hospitalized in Urmia city. This cross-sectional study was conducted in West Azerbaijan province, Iran. According to the daily report from the meteorology center of West Azarbaijan province, the data on the concentrations of air pollutants, including PM10, NO2, O3, CO, and PM2.5 were extracted. Moreover, the files of patients without underlying risk factors hospitalized due to pulmonary embolism were extracted. Finally, admissions from 2 days before until 2 days after the polluted days were compared to hospitalizations on clean air days of the same month. Design: A cross-sectional study. Setting(s): Urmia, the capital city of the West Azerbaijan province in northwestern Iran. Participants: A total of 1275 patients without underlying risk factors hospitalized due to pulmonary embolism were included. Outcome measures: Admissions from 2 days before until 2 days after the polluted days were compared to hospitalizations on clean air days of the same month. Results: Out of 1779 patients admitted due to pulmonary embolism, 1275 patients met our inclusion and exclusion criteria. Based on the results, 403 patients (31.6%) were hospitalized in clean and healthy air (air quality index [AQI] of 0-50 and 50-100), 816 patients (64.1%) were hospitalized in unhealthy air (AQI: 150-101), and 56 patients (4.4%) were hospitalized in days with polluted air (AQI:151-200). According to Pearson’s correlation coefficient, there was a significant relationship between carbon monoxide (r=0.09, P=0.0001), sulfur dioxide (r=0.11, P=0.001), PM10 (r=0.28, P=0.001), and PM2.5 (r=0.45, P=0.0001) concentrations and the frequency of hospitalizations due to pulmonary embolism. Conclusions: There is a positive and significant relationship between air pollutants and the number of hospitalizations due to pulmonary embolism. Hence, preventive measures should be taken into account regarding the air pollution at the provincial and national levels.