The prevalence, distribution and location of dental caries were studied in the permanent dentition of skeletons from a large mediaeval cemetery, where successive phases of use could be distinguished. The main phases dated from 1240 AD to 1440 AD. During this 200-year period, caries prevalence showed a statistically significant linear trend to increase. There was an increase in caries prevalence with increasing age from age band 20–25 through 26–35 to 36–45, and this trend was statistically significant in all phase groups but one. The teeth attacked by caries were chiefly molars, followed by premolars, with a low rate of attack in incisors and canines. The differences in caries prevalence between these major tooth classes were, significant. Juveniles and adults presented different patterns of carious attack on tooth surfaces, occlusal surfaces being most frequently affected in juveniles, and approximal surfaces in adults. The overall caries prevalence in the mediaeval population of Whithorn was 6.4% of the teeth present, a figure similar to those published for other Scottish mediaeval groups, but lower than the caries prevalence in an English mediaeval group.