'Second look' surgery following primary intact canal wall mastoid surgery for cholesteatoma is considered mandatory for most cases in modern otological practice. The morbidity of the second look can be reduced by the use of the rigid otoendoscope. Forty-three patients undergoing 'second look' surgery were studied with an average age of 24.7 years. Prior to surgery a computed tomography (CT) scan was performed to assess the anatomy and pneumatisation of the cavity. The mean interval between primary and secondary surgery was 16 months and in all cases CT scans were performed within 6 months of 'second look' surgery. The presence of an opaque mastoid did not correlate with residual or recurrent cholesteatoma. The sensitivity of CT in diagnosing residual or recurrent cholesteatoma was 42.9% with a specificity of 48.3% and a predictive value of 28.6%. These results are explained by the fact that it is radiologically impossible to differentiate between recurrence, scar tissue or fluid with a CT scan. Nevertheless it was possible to inspect the cavity with the otoendoscope even in the presence of an opaque mastoid whether due to scar tissue or residual/recurrent cholesteatoma.