In this paper, we describe a patient with transient osteoporosis of the femoral condyle. A differential diagnosis should be made for osteonecrosis, infectious disorders, and infiltrative neoplasms based on the normal laboratory findings and diffuse bone edema pattern in MRI. Since this disorder is self-limiting, both the surgeon and clinician should be aware of this condition and must avoid unnecessary intervention. (C) 2002 Elsevier Science B.V. All rights reserved.