Caveat arthroplasty is arthroplasty undertaken to treat a presumed nonneoplastic disorder, which is later determined to be secondary to an extraarticular tumor. We identified 6 patients who had caveat arthroplasty before referral to our orthopedic oncology center. Three patients had completed arthroplasties at an average of 29 weeks before discovery of a neoplasm. Three arthroplasties were aborted after a neoplasm was discovered intraoperatively. Prearthroplasty radiographs of 4 patients were reviewed, all demonstrating evidence of malignancy. Caveat arthroplasty may be avoided if malignancy is considered preoperatively, particularly in patients with atypical symptoms, histories of cancer, and rapid periarticular bone loss. If a neoplasm is discovered intraoperatively, the arthroplasty should be aborted. Patients in whom malignancy is suspected should be referred to a musculoskeletal oncologist.