In this study, it was aimed to determine high school students' cognitive structures regarding to the immunity, infection, allergy and autoimmunity. In this study, it was tried to reveal the cognitive structures of high school students on immunity, infection, allergy and autoimmunity just before COVID-19. The study was carried out with 77 students. The data collection tool was Words Association Test. The data collection tool was prepared separately for each stimulus word which were immunity, infection, allergy and autoimmunity. These stimulus words were chosen since these are the subthemes of the Immune system in the Turkish Secondary Biology Curriculum. Data analysis was performed for each stimulus word. The content analysis and coding of the data resulted in the categorization of the data. Considering the categories, models of the students' cognitive structures were drawn. In addition, the correlation coefficient was calculated according to the similarity between the answers given to each stimulus word. As a result, in our study, it is seen that the basic concepts of immunity, infection, allergy and autoimmunity are not predominantly structured in the minds of the students. It is worrying that basic concepts such as antibodies, passive immunity, and T cells are very rare or absent in the study.