We describe six elderly cases of acute myositis with type A influenza virus infection (Sydney) during the 1998-1999 outbreak. All six cases suffered from myalgia or muscle weakness especially in the lower extremities and the serum creatine kinase (CK) values were elevated above 1,000 IU/l without MB isoenzymes or electrocardiogram abnormalities. There have been a few case reports of acute myositis associated with influenza virus infection in the elderly. However, we noticed a high incidence of acute myositis among elderly patients with type A influenza virus infection. This complication may occur more commonly in elderly patients than has previously been thought.