Background: The 11th revision of the International Classification of Diseases (ICD-11) aims to provide a new definition of adjustment disorder (AjD), which is one of the most frequently diagnosed disorders. Coronavirus disease (COVID-19) pandemic has affected the mental health of people and the associated stressors could lead to AjD. The study aimed to investigate the AjD symptoms during COVID-19 pandemic based on the ICD-11 concept on a clinical sample. Methodology: A cross-sectional observational study was conducted between June 10, 2020, and August 9, 2020, among patients visiting the outpatient department of the authors' institute. Prevalence rates of stressors due to COVID-19 and AjD were estimated using scale of the International AjD Questionnaire (IADQ). Results: The study enrolled 723 subjects and 638 subjects endorsed at least one psychological stressor. The IADQ algorithm showed that 25.24% (161) of subjects were suffering from AjD due to the COVID-19 pandemic with a mean score of 20.29 (standard deviation = 4.26) among them. The most common stressors were related to financial problems (81.03%), work problem (63.17%), and personal health problems (27.43%). Conclusion: The high proportion of AjD during COVID-19 in this study may reflect a need for specific interventions. Provision for health-care services for such individuals is essential to avoid other mental disorders in the future.