AIMS: We aimed to evaluate bilateral hearing function in patients undergoing primary unilateral stapedotomy, according to the 1995 American Academy of Otolaryngology, Head and Neck Surgery guidelines and the Glasgow benefit plot. We also aimed to analyse the effect of pre-operative hearing impairment type on post-stapedotomy hearing. STUDY DESIGN: Retrospective chart review. METHODS: Medical records relating to 1369 stapedotomies performed by the senior author (JJH) from 1991 to 2006 were reviewed. Seven hundred and fifty-one patients undergoing primary unilateral stapedotomy were included. Hearing results for these patients were evaluated according to the criteria of the 1995 American Academy of Otolaryngology, Head and Neck Surgery Committee on Hearing and Equilibrium guidelines, and the Glasgow benefit plot. Subgroups of patients with pre-operative unilateral, bilateral symmetrical and bilateral asymmetrical hearing loss were separately analysed. RESULTS: The most successful results, as regards the achievement of bilateral, socially serviceable hearing, were demonstrated in patients with unilateral hearing loss; 78 per cent of these patients had normal hearing post-operatively. Overall, patients' achievement of bilateral, socially serviceable hearing correlated highly with their type of pre-operative hearing impairment (r = 0.74). Normal post-operative hearing levels also correlated with pre-operative bone conduction (r = 0.61). CONCLUSION: This study represents the largest reported series of primary stapedotomy cases evaluated with the Glasgow benefit plot. Patients' bilateral post-operative hearing function depended on their type of pre-operative hearing impairment. Pre-operative bone conduction thresholds, corrected for Carhart's effect, were useful in predicting achievable post-operative air conduction.