A 46-month-old boy with a four-day history of pain and swelling over the right posterior ilium was thought to have acute osteomyelitis on the basis of a normal pelvic x-ray, markedly increased scintigraphic activity in the right ilium, and a mildly elevated sedimentation rate. At surgery, no signs of osteomyelitis were found, and biopsy revealed osteolytic osteogenic sarcoma. This is the youngest child with osteogenic sarcoma of the pelvic reported in the literature.