Aims To assess the relationship between oral health status and Body Mass Index.Material and methods This paper relates to the free-living sample (participants who lived in their own home, rather than an institution) of the National Diet and Nutrition Survey: people aged 65 years and older. Subjects: 629 adults.Data collection A probability random national sample of adults who had a dental examination, an interview and an anthropometric examination.Data analysis Fisher's exact test and multivariate logistic modelling.Findings Being underweight was relatively uncommon in this population. People without teeth were significantly (P=0.05) more likely to be underweight than those with 11 or more teeth; 12.3% and 2.9%. A highly statistically significant (P=0.001) difference was observed in BMI between dentate people with 1–10 teeth and with more than 10 teeth; 24% and 2.9% were underweight. Dentate people with less than 21 natural teeth were on average more than 3 times more likely to be obese than those with 21–32 teeth (P=0.036). There was no significant difference in both the proportion of overweight and obese adults between those who were edentulous and dentate with 21 or more teeth. A similar pattern was observed when the number of posterior occluding pairs was compared with BMI categories. Results of multiple logistic regression were adjusted for the confounding effects of age, social class, region of origin and partial denture wearing.Conclusions Older people in Britain with more than 20 teeth are more likely to have a normal Body Mass Index.