The temporomandibular joint condyle is susceptible to developing a variety of problems, ranging from simple osteoarthrosis to severe condylar resorption. This article will focus on issues related to the etiology of these conditions. Condylar resorption (also known as condylysis) is an event rarely seen in normal orthodontic practice, but when it occurs, it is a very unhappy occurrence and often puzzling and inexplicable. This phenomenon represents an aggressive and fast-moving form of degenerative joint disease. As will be discussed in this article, many cases of temporomandibular joint degenerative joint disease arise from specific local or systemic etiologies, but others (especially condylysis) have been described as "idiopathic." It is the authors' opinion that the term "idiopathic" might be too easily used as an explanation. When something happens, there is usually a reason, but often it is not known what that reason is. Hence, the term "idiopathic" is used as a quick and easy explanation for the occurrence rather than investigating deeper to find the real cause of the problem. Certainly, the cause cannot be found in every case, but there are more areas to investigate than many are aware of, and some of those will be presented here. © 2013 Elsevier Inc.