Objectives: The COVID-19 outbreak is an example of a crisis that triggered an increase in generalized anxiety disorder. The study aims to validate the Polish version of the Generalized Anxiety Disorder 7-item scale (GAD-7) by Spitzer et al. among a non-clinical sample of employees and examine the invariance depending on the gender and age of working adults. Material and Methods: For assessing factor structure of the Polish version of the GAD-7, the data were collected from a sample of 821 adults employed in 4 economic sectors (health care, education, IT, public administration) during the initial phase of the COVID-19 pandemic in Poland (April 10–May 24, 2020). Due to differences in the severity of GAD symptoms across gender and age groups, the measurement invariance in these groups was tested. Results: The results of a series of confirmatory factor analyses confirmed the unidimensionality of the GAD-7. The values of the composite reliability index and Cronbach’s α showed that it is a reliable tool. The GAD levels demonstrated strong relationships with professional burnout, psychological distress, and psychological complaints. These relationships were stronger than the relationships between these factors and job satisfaction. Construct, metric and scalar invariance across gender and age groups were documented. Women experienced more severe symptoms of generalized anxiety disorder than men. Generalized anxiety disorder affected 28% of respondents. Conclusions: This study contributes evidence of the validation of the GAD among employees and also confirms the invariance depending on gender and age. The Polish version of the GAD-7 has good psychometric properties in a group of professionals and can be recommended for research and to be used in an occupational medicine practice, especially during crisis periods associated with the risk of developing a generalized anxiety disorder. Int J Occup Med Environ Health. 2023;36(4):493–504