A prospective study of 55 ossiculoplasty operations has been carried out. Mean pre- and post-operative air-bone gaps and the changes in mean hearing loss were determined using the frequencies 500, 1000 and 2000 Hz. The influence of six potentially relevant variables on hearing results has been studied. Univariate analysis suggested that both the loss of the stapes arch and the presence of a mastoid cavity were associated with a significantly poorer outcome, but multi-variate analysis confirmed this for loss of the stapes arch only (P = < 0.01). This is probably because the patients with open mastoid cavities more commonly suffered loss of the stapes arch (55%) than those with no cavity (27%) and had significantly larger air-bone gaps pre-operatively than those with no cavities (P = < 0.008). The results confirm the paramount importance of loss of the stapes arch as a determinant of outcome in ossiculoplasty and highlight the difficulties associated with trying to make valid comparisons between different patient groups undergoing this type of surgery.