An epidemiological survey in 12 cantons of Switzerland yielded a high percentage of all the sites examined with signs of gingivitis. Nevertheless, only 4% of all the sites showed periodontal breakdown of 7 mm or more; however, those sites were distributed in larger proportions of the population sample. Further frequency analysis revealed that more than 75% of the persons examined yielded no or only few sites with periodontal breakdown. The results of this study indicate that despite the high percentage of inflamed gingival units in the population, periodontal breakdown is less frequent than commonly estimated.