The aim was to establish diagnostic standards for primary approximal radiographic caries diagnosis. These were described with reference to ranking of subjects, mean "intermediate" score per subject, which was based on the majority diagnosis recorded by three examiners, and by category of a certainty scale for individual tooth surface scores. The results recorded by two fourth year dental students ... [Show full abstract] and two hygienists, when reading 40 pairs of posterior bitewing radiographs of children between 13 and 15 years of age, showed an acceptable level of agreement for ranking of subjects. Agreement was less satisfactory, when comparing the mean scores of these four examiners with the "intermediate" score per subject and with a standard for individual surfaces. The proposed standards do not represent true scores, but serve as guidelines, as they depend on the diagnostic level of the examiners on whose scores the standards are based, and on the diagnostic criteria employed.