A retrospective series is presented of 51 cases operated on for suspected perilymph fistula. In 26 ears a fistula was identified at surgery. A positive fistula test was found to strongly indicate a perilymph fistula but was more often negative than positive in surgically demonstrated fistula ears. Other vestibular tests were found to be of little value in the pre-operative diagnosis. Ears with a surgically demonstrated fistula and sensorineural hearing loss had either flat or downward-sloping audiograms. Difficulties in diagnosing a perilymph fistula at tympanotomy are discussed. At follow-up, vestibular symptoms were found to be eliminated or improved in 96 per cent of cases with surgically demonstrated fistulae and in 68 per cent of cases in which no fistula was detected at tympanotomy but hearing improved significantly in only one ear (4 per cent) of the former group and in five ears (20 per cent) of the latter group.