Oroantral fistula (OAF) is an uncommon complication in oral surgery. About 5% of all extractions of maxillary premolars or molars may result in communication to the antrum. Small fistulae, 1-5 mm in diameter may close spontaneously, but larger fistulae usually require surgical closure. Pre-operative determination of the size of the fistula is often unreliable leading to difficulties in planning subsequent clinical management. We report a method for the precise determination of the size of the OAF using a dental computed tomography (CT) software program.