Cartilage defects of the knee joint may be either isolated or in conjunction with various disorders of the knee. There are no clinical complaints and physical findings specific for joint defects. In addition, except for some magnetic resonance imaging techniques, there are no specific imaging methods for diagnosis. Therefore, arthroscopic evaluation is the gold standard for the diagnosis. Although there are many studies on the treatment of cartilage defects, natural course of the defects has been evaluated in only a few studies. Furthermore, controversy exists as to how and in which direction different treatment methods affect the natural course of cartilage defects. This review addresses factors affecting the natural course of cartilage defects; yet, the exact indications, timing, and methods of treatment, and whether any treatment is necessary remain unclear. Prospective, randomized, and controlled studies are needed to evaluate the results of different treatment methods on the natural course of cartilage defects.