It is commonly stated that operative closure of large perforations of the tympanic membrane is less successful than closure of small perforations. Few authors mention the exact size of the perforations studied, and fewer still give their method of measuring perforations. We describe a photographic method of assessing the size of perforations relative to the total drumhead, measuring them with a computerized digitizing pad. Thirteen temporal bones were selected at random. Perforations of different sizes, shapes and at different sites were fashioned in the tympanic membranes. These were assessed by clinicians of all grades, who were asked to draw the perforations and give estimates of the perforation size as a percentage of the total drumhead. Visual estimates and drawings were compared with a photographic objective method. Gross errors (some in excess of 100%) were apparent in both estimates and drawings. There was a highly significant statistical difference between the objective method and visual estimates and drawings (P < 0.001). Greater clinical experience was not correlated with better performance in estimating the size of perforations.