Limb-salvage surgery for malignant tumors frequently involves reconstruction with an endoprosthesis anchored to bone by using third-generation cementing techniques. A 10-year-old boy with osteosarcoma had a pulmonary embolus caused by polymethylmethacrylate after having limb-salvage surgery that used high-pressure cementing techniques. He experienced transient postoperative chest pain, and a new wedge-shaped radiodense pulmonary lesion appeared on a computed tomography scan of the chest. A thoracotomy for resection of suspected metastatic osteosarcoma revealed a pulmonary infarct caused by cement embolization. Awareness of this potential complication should prompt investigation of possible pulmonary embolism and may prevent unnecessary thoracotomy.