Although the hearing loss of patients with Treacher Collins syndrome is well documented, few studies have reported jointly on their hearing loss and ear pathology. This paper reports on the hearing loss and computerized tomography (CT) assessments of ear malformations in a large pediatric series of patients with Treacher Collins. Of the 29 subjects assessed by the Craniofacial Program between 1986 and 1990, paired audiologic and complete CT assessments were available for 23 subjects. The external ear canal abnormalities were largely symmetric, either bilaterally stenotic or atretic. In most cases, the middle ear cavity was bilaterally hypoplastic and dysmorphic, and ossicles were symmetrically dysmorphic or missing. Inner ear structures were normal in all patients. The majority of patients had a unilateral or bilateral moderate or greater degree of hearing loss and almost half had an asymmetric hearing loss. The hearing loss of all subjects was conductive, except for three whose loss was bilateral mixed. Two types of bilaterally symmetric hearing loss configurations, flat and reverse sloping, were noted. Conductive hearing loss in patients with Treacher Collins is mainly attributable to their middle ear malformations, which are similar for those of patients with malformed or missing ossicles.