A 30-year-old Thai woman with piriformis pyomyositis presented with sciatica. Computed tomography showed swelling and enhancement of the right gluteus medius and piriformis muscles. She made a complete recovery after a course of intravenous antibiotics. This condition has only been reported three other times and is often diagnosed with difficulty. It could be erroneously dismissed as a lumbar disc prolapse. If untreated, it could lead to prolonged hospital stay and death. A high index of suspicion, early diagnosis and appropriate antibiotic or surgical treatment leads to full recovery.