To investigate the clinical and behavioural factors indicating root caries risk among older people. Cross-sectional clinical and interview data from the National Diet and Nutrition Survey (aged 65 years and over) in Great Britain. Logistic regression models of the prevalence of root caries and linear regression models of the extent of root caries were constructed to quantify the role of a range of clinical and behavioural risk indicators, including sugars intake. A national sample of older British adults, free-living and institutionalised. 462 dentate adults aged 65 years or over. Nine or more intakes of sugars per day more than doubled the odds of root caries being present (OR 2.2-2.4). Other clinical and behavioural factors affecting root caries included wearing a partial denture in the presence of heavy plaque deposits (OR 2.1-2.6) and infrequent tooth brushing (OR 2.8-4.1). Linear regression models showed that, amongst those that had root caries, sucking sweets in the presence of a dry mouth, poor hygiene, partial dentures and living in an institution contributed to the extent of root caries, as measured by the RCI(d). Of the factors open to possible clinical or behavioural intervention, frequent sugars intake, poor hygiene and partial dentures were all associated with large increases in risk.