Osteonecrosis of the knee is a rare complication following arthroscopic surgery. Little is known about its etiology. The most important differential diagnosis is preexisting and undiagnosed early-stage spontaneous osteonecrosis of the knee. Medicolegally, arthroscopic surgery could be wrongly regarded as the primary cause for postarthroscopic osteonecrosis. Orthopedic surgeons need to be aware of the diagnostic pitfalls in differentiating between these entities. We suggest that the descriptive term "osteonecrosis in the postoperative knee" should be used rather than the captious term "postarthroscopic osteonecrosis."