A 45-year-old man visited the first hospital complained of high fever on January 2003. He was diagnosed as having Influenza virus type A infection and prescribed of Oseltamivir. He was afebrile next day, but severe myalgia of neck, shoulder, lumbar region and right femoral region was appeared. His illness was considered as polymyalgia rheumatica and started of oral steroid therapy. His symptom was deteriorated and transferred to our hospital. Echography, Ga scintigraphy, computed tomography and magnetic resonance imaging revealed the multiple abscesses and the diagnosis of pyomyositis was made. Pyomyositis following Influenza virus infection must be considered as a differential diagnosis of myalgia after Influenza virus infection.