Background. Often with some infectious diseases, in addition to the typical manifestations, characteristic inflammatory changes are observed on the mucous membranes, which can imitate the course of other diseases. The purpose was to remind dentists and general practitioners about the importance of differential diagnosis of lesions of the oral mucosa in infectious and non-infectious pathologies on the example of clinical cases. Materials and methods. We conducted an empirical, descriptive study of 3 clinical cases of lesions of the oral mucosa in children who underwent inpatient treatment at the Kyiv City Children’s Clinical Infectious Hospital in 2023–2024. Results. In the first clinical case, the manifestation of type 1 diabetes was described, which was accompanied by oral candidiasis that was previously regarded as a suspicion of measles. The second clinical case demonstrates aphthous ulcers in HIV infection, which was previously mistaken for acute tonsillitis in a child. The third case described enteroviral vesicular stomatitis, which by the nature of the elements resembled chicken pox. Conclusions. Lesions of the oral mucosa can mimic the manifestations of common infectious and non-infectious diseases. Therefore, differential diagnosis of lesions of the oral mucosa is extremely important in various fields of medicine and dentistry.