The foundation of mastoid surgery for cholesteatoma has traditionally been a thorough knowledge of the anatomy and familiarity with landmarks, constant alertness to detect unsuspected complications and the experience to tailor the surgery to the pathology encountered. Whilst not indispensable, computed tomography (CT) scanning is a useful adjunct whose potential predictive value is only truly appreciated by skilled interpretation. We present a guide to analysis to maximize the value of pre-operative radiology.