The Danish nationwide oral health registration system is a system where information is collected by many observers. As the registration system has been the basis for several papers, an estimation of the consistency of its information seems relevant. The present study attempted to determine types and frequencies of inconsistencies in the caries recordings of the system, expressed as reversals in tooth or surface status. Recordings from two subsequent registrations of a random sample of 2189 individuals were compared surface by surface, in all, 209 791 surfaces. The overall frequency of impossible changes in tooth status for permanent teeth was 0.9%, varying from 0.3% for molars to 2.8% for premolars. The frequency of impossible changes in surface score from first to second recording were 5.8% for the primary and 5.9% for the permanent dentition. The frequency varied with both tooth surface and score at first examination.