A noninvasive optical method using an operating microscope was developed to measure the length of an ear canal under both open and occluded conditions. The method is based on the optical measurement of the distance between a reference point at the eardrum and a second point on the lateral aspect of an earmold-occluded ear canal. To estimate the occluded canal length, the length of the earmold is then subtracted from results of the previous measurement. The method was also used to determine the open ear canal length (the lateral reference point was the ear canal entrance), and averaged results agreed closely with previously reported data.