Purpose: To investigate the prevalence and distribution of marginal bone loss in the Danish population. Materials and Methods: Six hundred and sixteen randomly selected Danish adults (304 females and 312 males), mean age of 42 years (range 21-63 years) underwent a full-mouth radiographic survey consisting of 14 periapicals and two bitewings. The marginal bone level was measured with a digital caliper in mm, rounded off to the nearest 0.1 mm. The measurements were performed at the mesial and distal aspect of the tooth, from the cemento-enamel junction to the marginal bone. These measurements were used to calculate the marginal bone level (A) in mm for each tooth and each patient. Three thresholds were defined: normal marginal bone level (A 3 mm), borderline marginal bone level (3 mm = A 4 mm) and reduced marginal bone level (A >= 4 mm). Results: The prevalence of reduced marginal bone level in the individual and the frequency of teeth with reduced marginal bone level were almost similar. A reduced marginal bone level was evenly distributed among the tooth groups. Approximately 12% had reduced marginal bone level, 12% were in the borderline marginal bone level group, and the remaining 76% had a normal marginal bone level. The marginal bone level was ever more reduced with increasing age. No significant difference in bone level was observed between genders. Conclusions: The prevalence of reduced marginal bone level in a random Danish population is approximately 12% and is comparable to findings in other European countries. Schlagwörter: cross-sectional study, epidemiology, marginal bone level, prevalence, radiology