On the basis of observations of 393 patients over many years, the author considers it possible to distinguish 5 types among the various forms of the syndrome of branchial arches 1 and 2. Two types are characteristic of the syndrome of branchial arch 1: the mandibular type and the mandibuloauricular type. The former is unilateral and occurs very rarely, the latter is encountered more frequently and can be unilateral or bilateral. For the syndrome of branchial arches 1 and 2, three types are characteristic: the auricular, the mandibulofacial and auricular, and the craniofacial, articular and auricular. The auricular type is mainly characterized by marked anomalies of the cochlea and the sense of hearing, occurs most frequently of all and is also bilateral. The mandibulofacial and auricular type exhibits more pronounced affections of both the cochlea and hearing and the bones of the facial skeleton. It occurs frequently and is unilateral. The craniofacial, articular and auricular type shows the most serious combinations of defects of the cochlea, the base of skull, the temporal bone, the facial skeleton, and the absence of the branch and the condylar process of mandible as well as hypoplasia of the soft tissues of the face. Systemic dysplasias of the face, the jaws and the cochlea are combined with defects of other, frequently distant, systems.