The distribution of caries in the dentitions of 108 crania and 140 mandibles of victims of the Great Plague of London (1665) was determined and compared with that previously established for dentitions of the Iron Age, Roman, Saxon, and Mediaeval periods in Britain. By the 17th century the overall prevalence of caries was considerably greater than in the earlier periods, and the pattern of attack had become recognizably similar to that occurring in the modern British population. Caries at contact areas, which was rare in the preceding periods, had increased to become the most frequent site of attack on the interstitial surfaces (this change was presaged in findings for the Middle Ages where the number of cavities at contact areas had increased somewhat, although the data were insufficient to show this as a statistically significant trend). The frequency of cavities in occlusal fissures had also increased considerably. There was no corresponding rise in the caries rate at interstitial cemento-enamel junctions. These changes in the pattern of caries distribution correlate well with the changes known to have occurred in the British diet between the late Middle Ages and 17th century – especially the greater consumption of refined carbohydrate.