Staphylococcus epidermidis is a common cause of infections associated with prosthetic devices and immunocompromised patients. Spontaneous pyomyositis due to the above pathogen is very uncommon. Kikuchi-Fujimoto disease (KFD) is a subacute necrotizing lymphadenitis, first described in Japan. A T cell-mediated hyperimmune response to various pathogens in a genetically susceptible individual has been primarily been considered in its pathogenesis. We report a patient who developed spontaneous pyomyositis caused by S. epidermidis concurrently with KFD, and discuss the possibility of S. epidermidis infection being the stimulant of KFD.