Congenital dysplasias of the labyrinth of the inner ear are associated with varying degrees of hearing loss. There is a risk of a fistulous communication between the subarachnoid space and the middle ear cavity in some cases that present either as cerebrospinal fluid otorhinorrhea or as recurrent attacks of meningitis. The types of deformity where such a fistula is likely have not been clearly defined. The authors correlated the hearing state with the imaging assessment in 20 patients with congenital malformation of the labyrinth and, in particular, the cochlea. In addition the postmortem histologic findings from one patient with severe cochlear dysplasia who died from otogenic meningitis are described. The key to the assessment is the basal turn of the cochlea. If the basal turn is present and of normal caliber then some hearing is possible and there is no risk of a major fistula. However, if the basal turn is wider than normal or replaced by an undeveloped sac then there is anacusis and very real risk of fistula. In such cases the deformed labyrinth needs to be packed with fibrofatty tissues after just one attack of meningitis.