The purpose of the study was to assess the degree of marginal alveolar bone loss and tooth loss in a longitudinal study over a period of 20 years. In 1970 a medical and odontological study on a stratified sample of the population of the County of Stockholm aged 18-65 years started. Twenty years later a new odontological investigation was performed on the 513 subjects who wanted to take part once more and who had at least five remaining teeth. The mean distance between the marginal bone level and the cemento-enamel junction measured on the radiographs in 1970 (MBL) was 13.8% of the root length. The mean bone loss during the 20-year period (MBD) was about 10%, corresponding to a mean annual marginal bone loss of about 0.1 mm. The MBD-values were significantly positively correlated to the MBL-values. The mean number of remaining teeth was 24.7 in 1970 and 21.8 in 1990. A significant positive correlation existed between the number of teeth lost between 1970 and 1990 and the mean MBD-value. In stepwise multiple regression analyses, the MBL-value was the only independent variable positively correlated to the MBD-value, while the number of teeth lost between 1970 and 1990 was significantly correlated to age and the MBL-value.