Infections caused by Fusobacterium species are rare; however serious infections with complications or mortality may occur occasionally. We conducted a retrospective study to investigate the clinical features of patients with Fusobacterium infections and the differences between infections caused by the species F. necrophorum, F. nucleatum, and F. varium. Additionally, we attempted to identify risk factors for Fusobacterium-associated mortality. This study included all patients at a large tertiary care teaching hospital in South Korea with Fusobacterium infections from January 2006 to April 2021. Demographic, clinical, laboratory, and outcome data were analyzed. Multiple logistic regression analysis was performed to assess the risk factors for in-hospital mortality associated with F. nucleatum and F. varium infections. We identified 272 patients with Fusobacterium infections during the study period. The number of Fusobacterium cases has increased recently, with F. varium infections markedly increasing since 2016 and causing a significant proportion of infections. Patients with F. varium infections were older and had a higher proportion of nosocomial infections than the other groups. The F. nucleatum and F. varium groups showed higher in-hospital mortality than the F. necrophorum group. Through logistic regression analysis, APACHE II score and serum albumin level were considered risk factors for in-hospital mortality. APACHE II score was positively correlated with age, red cell distribution width, and serum blood urea nitrogen, and negatively correlated with serum albumin level. Infections caused by Fusobacterium species are increasing. F. varium causes a significant proportion of severe infections.