The efficacy of two oral hygiene training programs on the control of plaque and the prevention of gingival inflammation in adolescents was evaluated during a 3-year period. A population of 227 Brazilian schoolchildren were divided into 3 groups. The first group received a comprehensive program based on individual needs and included information sessions pertaining to the etiology and prevention of dental diseases together with extensive training in self-diagnosis and oral hygiene. In addition, an information session was arranged for parents and teachers of these children. The second group received a less comprehensive program consisting of conventional oral hygiene training. The third group (control) received no preventive program. The programs were presented through frequent initial training sessions ensued by infrequent follow-up visits. During the experimental period, the two oral hygiene training programs involved 3.5 and 1.5 hours per child, respectively. The children were examined clinically at baseline and annually over the next 3 years to assess plaque and gingival bleeding and the data were analyzed by a multi-level variance component analysis. All children showed a perpetual improvement in their oral hygiene and gingival state during the course of the study. However, the improvements observed in the comprehensive group were significantly better than that of the control group. Results from the less comprehensive group were not significantly different from the control group. Longer exposure to the programs appeared to produce more improvement; children with higher plaque and gingivitis scores prior to the program showed less favorable results; girls exhibited better results than boys.(ABSTRACT TRUNCATED AT 250 WORDS)