This study demonstrates that the size of the gonial angle can be determined from the orthopantomogram with the same degree of accuracy as from the generally used lateral cephalogram, the gonial angle being formed by the tangents of the lower border of the mandible and the distal border of the ascending ramus and the condyle on each side. It also shows that the right and left gonial angles can be quite easily determined individually from orthopantomograms, thus avoiding the disturbing influence of the superimposed images found on lateral cephalograms. It proves conclusively that the orthopantomogram is the more obvious choice for determination of the gonial angles.