This study was designed to develop a method of transferring gonion from lat
eral to frontal cephalograms, and to use this method as gold standard when
evaluating observer performance in identifying gonion in frontal cephalogra
ms. Observer ability to identify antegonion was also evaluated. There was a
range of 28 mm in the observers' identification of gonion and a statistica
lly significant deviation from gold standard. The factors "observer" and "c
ephalogram," regarded as random effects in an ANOVA analysis, and their int
eraction, each influenced the result, P < .001. The deviation from the mean
of all observations for antegonion ranged 8 mm with "cephalogram" having a
statistically significant influence. The results suggest that neither goni
on nor antegonion can be routinely used as valid landmarks in frontal cepha
lograms. Gonion can, however, be used if first identified in a lateral ceph
alogram and transferred to a paired frontal cephalogram aided by radiograph
ic indicators combined with a bilateral scrutiny of projection geometry in
different planes through gonion and indicator.