This paper examines the impact of the COVID-19 pandemic on the level of stress among health care workers employed in public health institutes in the Republic of Croatia. The paper aims to determine whether the COVID-19 pandemic affected the increase of stress levels compared to the pre-pandemic period among health care workers employed in public health institutes in the Republic of Croatia. It also aims to examine the physical and emotional manifestations of stress which occurred as a result of working in a time of pandemic, as well as determine whether health care workers of public health institutes who were in close contact with COVID-19 patients and infectious materials felt higher levels of stress compared to their colleagues who were not in close contact with the aforementioned. Research was conducted retrospectively, during September 2022, by means of an online survey on Google Forms. The translated and adapted Nursing Stress Scale and the adapted Oldenburg Burnout Inventory, as well as claims which were verified and approved by mentors were used. The questionnaire consisted of an introductory message, a list of questions, and a thank-you message. The obtained data were processed with the help of the SPSS software program. The results significantly deviated from the standard distribution of results and, as such, were indicative of the stress experienced before and after the COVID-19 pandemic. There was no statistically significant difference between stress levels experienced before and after the pandemic among participants who did not work with COVID-19 patients and who worked daily, nor among men and women. There was no statistically significant difference between stress levels experienced before and after the pandemic with respect to years of service. A statistically significant difference was found when comparing the stress levels experienced before and after the pandemic.