Objective: The aim of this study was to evaluate the initial and longer term success of closing the air-bone gap (ABG) to 20 dB in ossiculoplasty with canal wall down mastoidectomy. Methods: This study was conducted at a private otologic practice. Patients included those who underwent ossiculoplasty from 1989 to 1996 with canal wall down mastoidectomy, whether primary or revision (33 from a total of 387 tympanomastoidectomies). Outcome measures included ABG closure, long-term hearing stability, mastoid appearance, extrusion, and sensorineural hearing loss. Results: Almost 64% of ABGs were closed to within 20 dB. The mean pure-tone average improvement was 12.3 dB. The mean PTA hearing decline in the years after surgery was slightly less than 1 dB/year. Conclusion: Hearing improvement with a stable long-term hearing result is possible with canal wall down mastoidectomy. The potential for hearing gain is greatest for patients having larger preoperative ABGs. (Otolaryngol Head Neck Surg 2000;123:30-3.)