This survey documents the meagerness of teenagers' knowledge and behavior about dental health. They knew that brushing before bed and checkups are desirable. Otherwise, they were sorely lacking in fundamental knowledge about what is needed for optimum oral health. Except for 6 of the 2,517 sophomores, there was no evidence that they knew about plaque. Small minorities thought about using floss and then for removal of food, not plaque. Fewer than a fourth knew that periodontal disease was a disease of the gingiva. Brushing was the major oral health practice. But it was rarely checked with disclosing tablets and mouth mirrors. It is questionable whether most knew about these. Flossing was rarely done. Curtailment of sweet foods or drinks as an oral health measure was even rarer. One would expect some improvement in the six years since this study was done, given the greater emphasis on plaque control in dentistry. Yet, the possibility that many more of a similar group of teenagers at this time would be preventively oriented seems unlikely. Plaque control programs are not that common in dentistry. And only 42% of the sample studied could be said to go to the dentist for preventive checkups in the first place. Morever, recent interviews I have done with patients at a public clinic did not uncover much awareness or behaviors related to plaque control. The respondents in the study reported here were students in their tenth year of public school. Their schooling was preparing them for many things, including common problems of everyday life. Very few problems are as common as tooth decay and periodontal disease. Yet the teenagers knew little about and were doing relatively little to prevent these problems. Obviously, their need for instruction is great.