Symptoms of psoas muscular abscess in children are nonespecific and differential diagnosis is made among diseases included in children's acute hip pain syndrome, imaging tests being necessary for diagnostic confirmation. During the first semester of 1995, 48550 children were examined in Pronto Socorro do Instituto da Criança do Hospital das Clínicas da Faculdade de Medicina da Universidade de São Paulo, four of them diagnosed as having psoas muscular abscess (2 females and 2 males, ages varying from 1 to 12 years). All of them had nonespecific clinical features and diagnosis was confirmed by abdominal ultrasound and/or computerized tomography. Staphylococcus aureus was isolated as the etiologic agent in 3 children, findings similar to the ones in literature.