The anatomic results of mastoid obliteration surgery on 54 ears during the past 10 years were analyzed, and the comparative utility of several materials for obliteration was evaluated. Thirty-three ears had primary chronic otitis media with or without cholesteatoma (group 1), and 21 ears had old open mastoid with intractable chronic discharge due to incomplete epithelialization (group 2). The materials used for obliteration were biologic (pedicled muscle flap, autogenous bone chips, tragal cartilage with perichondrium, allograft dura), nonbiologic (hydroxyapatite), or a combination of two of these materials. Evaluation at 2 months postoperatively showed that 42 ears were anatomically complete, whereas the other 12 ears were incomplete: three cases in group 1 and nine cases in group 2. The main causes of these unsatisfactory results were exposure of transplanted artificial material or partial loss of the pedicled muscle flap. In the long-term follow-up results, four ears were evaluated as unsatisfactory in group 1, and six ears in group 2, owing to shrinkage of obliterated tissue. The major causes of failure were anatomic incompleteness following surgery for old open mastoid cavity, in which the use of biologic materials for obliteration was much safer than nonbiologic material, and from the protrusion of artificial materials used.