Improved knowledge of "normal" temporomandibular joint function and morphology is a basic requisite for the recognition and diagnosis of TMJ abnormalities. Indeed, until such knowledge exists, care must be exercised in the clinical, radiographic, arthrographic, and histologic diagnosis of abnormal temporomandibular structure and/or function. This article discusses variations in TMJ function and morphology in Class I persons and those with skeletal Class II open-bite and Class II deep-bite dentofacial morphologies. These differences are explained on the basis of accepted principles of biomechanics and its influences on cartilaginous growth and bone modeling.