We report three children who were treated for pyogenic infection of the sacroiliac joint. The disease, usually present in late childhood or adolescence, is uncommon and difficult to assess so that the diagnosis is usually delayed. The three patients were two boys and one girl, aged 14, 15 and 12 years, respectively. A detailed history and physical examination are very important for establishment of the diagnosis. All the three cases presented with typical clinical triad of fever, limping gait and buttock pain. Pelvis compression maneuver, which directly stresses the sacroiliac joint, may aggravate the joint pain and suggest this diagnosis. On physical examination, this test is positive in all our cases. Nuclear scintigraphy is useful for localization of early lesions. For detecting abscess formation, magnetic resonance imaging was performed in two cases and computed tomography in one. In one of the patients, computed tomography failed to demonstrate an iliopsoas abscess formation, which was proved by magnetic resonance imaging later. Staphylococcus aureus was isolated from blood in all three patients. Prompt antibiotic therapy reduces complication and operation is rarely needed. With rapid and appropriate medical treatment, all our patients recovered without an sequelae.