Sacroiliac joint infection is relatively rare and difficult in differential diagnosis with other spinal disorders. Delay in diagnosis is frequent which causes an increased morbidity. The authors reviewed clinical courses of the patients who were treated for pyogenic sacroiliac joint infection from January 1985 to April 1997. Investigation included physical examination, bone scan, biopsy, ESR, plain radiography, CT scan, and MRI. The diagnosis was made on clinical findings and a positive results of the above investigation. There were 17 pyogenic arthritis. Six patients had all symptoms of triad(fever, unilateral buttock pain, limping gait) and fifteen patients had typical buttock pain. Increased ESR(>20mm/hr) was noticed in fourteen patients. In all seventeen cases, skeletal scintigraphy and Gaenslen test were positive. Also CT scan and MRI study were helpful in diagnosis of the sacroiliac joint infection. Pus culture could be done in twelve cases and staphylococcus aureus was found in seven cases. Conservative treatment was performed in eleven cases, and operation in six cases. Fifteen cases were recovered and two cases relieved.