Pneumonia is one of the most common causes of children’s hospitalization and death. The aim of the study was a medico-legal analysis of children who died suddenly due to pneumonia undiagnosed in their lifetime. The research was of a retrospective character and consisted in an analysis of prosecution files. The study included 47 children who died between 2011-2018 in whom pneumonia after post-mortem examination was indicated as the cause of death, as well as children in whom the cause of death, despite additional post-mortem examinations, including histopathological tests, was not established. In some cases, under additional post-mortem examinations, additional targeted immunohistochemical staining of selected lung sections was performed to establish the diagnosis. In children with prodromal symptoms, histopathological examination showed significantly more frequent atelectasis than in children without prodromal symptoms. Pneumonia is a significant clinical problem. Especially in young children, it may proceed with- out any symptoms that would cause such a diagnosis to be made. A properly conducted post-mortem diagnosis supplemented by immunohistochemical examinations allows to reduce the number of unexplained deaths in children.