A case of group B streptococcal pyomyositis The group B streptococcus is an opportunistic pathogen that causes a variety of serious infections including bacteremias, puerperal sepsis, and neonatal meningitis. Group B streptococcal infections of muscle are rare. We report here an unusual case of group B streptococcal pyomyositis. Pyomyositis arises predominantly from infections caused by Staphylococcus aureus and, occasionally, Streptococcus pyogenes. Because of the rarity of pyomyositis in temperate climates, the common lack of localizing signs or symptoms, and the frequently negative blood cultures, considerable delay often precedes the diagnosis of pyomyositis; in fact, the infection has been initially misdiagnosed as muscle hematoma, cellulitis, thrombophlebitis, osteomyelitis, or neoplasm. Diagnosis may be greatly aided by radiologic techniques that can demonstrate the sites of muscle enlargement and the presence of fluid collections. The response to antibiotics is usually rapid, but resolution of the infection may require aspiration of deeply situated muscle abscesses. This report describes a diabetic patient with an unusual presentation of pyomyositis that mimicked an acute abdomen. 