Clinical and radiographic experience as well as histological findings leave no doubt that the term "condylar hyperplasia" refers only to hyperplasia of the condyle alone and should therefore not be used to mean the two hemimandibular anomalies as is the case in the literature today. There are two basically different malformations of one side of the mandible which we call hemimandibular hyperplasia and hemimandibular elongation respectively. We are convinced that there exist pure and mixed forms of both growth anomalies because we have observed several such clinical cases. The stimulus for the abnormal growth either lies within the fibrocartilaginous layer or is produced by it. Different histological patterns within the condylar growth zone were seen in the two anomalies. The pathophysiological bases of the abnormal growth are discussed. They seem to contribute to the understanding of the normal and abnormal mandibular growth and consequently also of many of the mandibular anomalies. The explanations are demonstrated by the illustrations of some cases.