The objective of this study was to evaluate the precision of the horizontal and vertical linear dimensional measurements on orthopantomographic images. Different horizontal and vertical distances denoted by metal markers were measured on 25 dry mandibles. The same mandibles were then positioned in an orthopantomographic machine and their radiographic images were made. Measurements of the same distances were repeated on the panoramic images and compared to the results of the measurements on the dry mandibles. All results were statistically analyzed. The results showed significant difference between the magnification factor listed by the manufacturer and the calculated magnification factors, the latter being closer to 1.00. The study also showed that linear measurements made only on one side of panoramic images of mandibles were close to actual dimensions of dry mandibles, while the measurements which extended across the midline of mandibles were greatly enlarged due to large magnification factors.