The histopathologic findings of five patients with trisomy 18 syndrome are discribed. Three patients have low-set ears, and two have auricular malformations and atresia of the external auditory canals. The chief findings are as follows; aberrant course of the facial nerve with an obtuse angulation at the first genu (2 bones), malformed stapes (3 bones), shortened cochlea (3 bones), flattened cochlea with underdeveloped modiolus (6 bones), decreased spiral ganglion cell population (7 bones), enlarged vestibule (7 bones) and semicircular canal (8 bones). There can be seem bony atresia of the round window, which is unreported previously.
