The objective of this study was to assess the level of root caries in a population of diabetic adults. Diabetics are of special interest because they are alleged to be periodontally compromised and have atypical patterns of refined carbohydrate ingestion. Diabetic subjects were patients of the Joslin Diabetic Center in Boston and had significantly elevated blood glucose and glycosylated hemoglobin levels over at least a ten-year period. Eligible subjects had to be between the ages of 45 and 65 and have a minimum of ten teeth and three sites with recession. Data were collected on coronal caries, oral hygiene, gingivitis, pocket depth, recession, and root caries and were compared with data from control subjects from a larger non-diabetic study group. There were 88 diabetics and 185 controls with mean ages of 55.7 and 56.3 years, respectively. The groups were found to be similar with respect to the numbers of buccal surface sites with gingival recession and the numbers of carious root lesions. There was a distinct difference, however, with respect to restored root surfaces: 1.76 mean filled surfaces were observed in the controls, as compared with 0.49 in the diabetics. A Katz Root Caries Index (for which lesions are calculated as a percentage of the numbers of exposed root surfaces) was determined to be 15.2 for the controls and 7.1 for the diabetics. A reasonable inference is that these differences are the result of a restricted ingestion of refined carbohydrates by the diabetic group. This was confirmed by a dietary survey of subsamples from the diabetic and non-diabetic groups.