In 1911 the 4th volume of the book"Histological and histopathological articles on the cerebral cortex with special attention to the pathological anatomy of mental diseases" was produced by the editor Alzheimer. One of the chapters is entitled"The PERUSINI cases". In honour of Perusini's achievement the term Alzheimer's disease is also known as"La malattia di Alzheimer-Perusini" (The disease of Alzheimer-Perusini). This article gives a review of the scientific historical context of neurobiological research at the beginning of the twentieth century. It describes Perusini's career in science, his period at Alzheimer's laboratory and demonstrates Perusini's scientific merits.