Ukraine still has diphtheria. This infection is developed with toxins secreted by pathogens of three Corynebacteria species, such as Corynebacterium diphtheria, Corynebacterium ulcerans, and Corynebacterium pseudotuberculosis. In January 2024, for the first time in recent decade, a fatal case of diphtheria in a resident of the Kyiv oblast was registered in Ukraine. The results of laboratory testing showed the toxigenic microorganism Corynebacterium ulcerans. The diagnosis was established based on the results of the pathological and anatomical autopsy and confirmed by laboratory testing during the examination of sectional samples. When a woman sought medical attention with certain clinical signs, medical care personal did not collect biological samples from the patient for testing on the causative agents of respiratory diseases of viral or bacterial origin, and the primary diagnosis did not contain information about the warnings of diphtheria. This indicates a low alertness of doctors regarding the possibility of the occurrence and spread of diphtheria. The anti-vaccination attitude of the population and migration processes under martial law contribute to a decrease in the level of immunization in the Kyiv oblast and pose a threat to diphtheria outbreaks.