Möbius syndrome (MIM no. 157900) consists of a congenital paresis or paralysis of the VIIth cranial nerve, frequently accompanied by paralysis of other cranial nerves, orofacial and limb malformations, defects of the musculoskeletal system and mental retardation. Although most patients are sporadic cases, familial recurrence is not rare. Different pedigrees suggest different modes of inheritance. We performed linkage analysis in a large family with autosomal dominantly inherited Möbius syndrome, consisting essentially of asymmetric bilateral facial pareses. After exclusion of the candidate region for Möbius syndrome on 13q12.2-q13, we localized the gene to chromosome 3q21-22, indicating genetic heterogeneity of Möbius syndrome. This heterogeneity is further proven by the exclusion of both loci in a second family with Möbius syndrome.