The present report describes the result of a clinical trial in which a group of adults have been maintained on a proper oral hygiene standard over a 6-year period. In 1971--72, 375 individuals were recruited to a test group and 180 to a control group. During the 6 years of trial, 65 persons from the test group and 34 controls were lost. The patients were divided into three age groups; I less than 35 years, II 36--50 years, III greater than 50 years. The members of the test and control groups were first subjected to a Baseline examination which included assessments of oral hygiene, gingivitis, periodontal disease and caries. Following this examination all caries lesions were treated and ill-fitting dental restorations adjusted. Each patient was also given a detailed case presentation and a dental prophylaxis. The control group patients were not involved in any further dental health programs during the subsequent 6-year period. Once a year, however, they were recalled to a public dental health clinic for examination and received symptomatic dental treatment. The test group participants, on the other hand, were given a preventive treatment, repeated once every 2-3 months which included (1) instruction and practice in oral hygiene techniques and (2) meticulous prophylaxis. The patients were re-examined 3 and 6 years after the baseline examination. At the Follow-up examinations the parameters studied at the Baseline examination were recorded again. The findings demonstrated that a preventive program which stimulates individuals to adopt proper oral hygiene habits may resolve gingivitis and prevent progression of periodontal disease and caries. Traditional dental care, on the other hand, did not prevent the progression of caries and periodontitis in adults.