Background: The burden of chronic obstructive pulmonary disease (COPD) is quite high and its prevalence is increasing. We aimed to evaluate the correlation of COPD severity according to the American Thoracic Society (ATS) criteria with spirometric measurements in patients admitted to the emergency ward. Materials and Methods: In this cross-sectional descriptive study, 50 randomly selected patients with COPD admitted to the emergency ward in a tertiary care center were evaluated. The COPD severity according to the ATS criteria was measured and its association with spirometric findings was evaluated. The statistical analysis was performed by SPSS software and the Kendall's tau-b correlation test. Results: The mean age (±standard deviation) was 64.3 ± 11.3 years. Twelve percent were females and 88 percent were males. The COPD severity, according to the ATS criteria, was mild in 16%, moderate in 48%, severe in 32% and very severe in four percent. There was a statistically significant correlation between total lung capacity (TLC) and COPD severity (P=0.013, r=275). Besides, there was a statistically significant correlation between functional residual capacity (FRC) and COPD severity (P=0.022, r=255). Age, sex, and the other spirometric findings especially FEV1 and FVC had no association with COPD severity (P > 0.05). Conclusion: According to the obtained results, it is concluded that determining the COPD severity according to the ATS criteria may help the physicians to estimate the patients' prognosis and therapeutic planning. However, the spirometric measurements may not be replaced by ATS criteria.