This longitudinal study of randomly selected Norwegian students and academicians has shown that 50% of the 17-year olds have lost no periodontal support, and the other 50% exhibited slight localized loss of attachment primarily on buccal surfaces of first molars and first bicuspids of both jaws. At 21 all students show one or more of these lesions as well as loss of attachment on interproximal surfaces. At 30 years of age the mean cumulative loss is still less than 1 mm. As they approach 40 years of age the mean individual loss of attachment is slightly above 1.5 mm or 10% of the total periodontal support, and the mean annual rate of attachment loss is 0.08 for interproximal surfaces and 0.1 mm for buccal surfaces. No case of juvenile periodontitis (periodontosis) or adult aggressive periodontitis were seen in this population. Seventy percent of the 15-year-old Sri Lankans have no or very little loss of periodontal support. However, approximately 30% exhibit localized lesions measuring between 2 and 9 mm and more than 1% have one or more root surfaces with 10 mm loss of attachment or more. In this age group the lesions occur at the interproximal and buccal aspects of lower central incisors and in first molars of both jaws. At 30 years of age the mean loss of attachment is 3.11 mm and approximately 25% of the tea laborers have lesions extending 10 mm or more below the cemento-enamel junction. As the Sri Lankan approaches 40 years of age the mean loss of attachment is 4.50 mm and the mean rate of progress of the lesion is 0.20 mm per year for buccal surfaces and 0.30 mm for interproximal surfaces. This study suggests that without interference the periodontal lesion progresses at a relatively even pace and that the progress is continuous.