In this paper we present a study of 6 cases, running through three generations of a Dutch family, with alternating Bell's palsy in an autosomal dominant mode of inheritance. The study included medical history data, neurological examination, blood glucose tests, electromyography, orbicularis oculi reflexes and radiological investigation. In 3 cases a bilateral hypoplasia or scanty cellularization of the mastoid bone and a unilateral obtuse tip of the petrous part of the temporal bones were found. These findings may be a potential inherited etiologic factor.