Background: Oral malodor (halitosis or bad breath) might be an important motivation tool for improving oral health in adolescents. There are few studies that report the epidemiology of oral malodor in high school students and the relationships with lifestyle and oral health status. This research was conducted to obtain underlying data for introducing an oral health education program which targeted prevention of oral malodor as a motivation tool for changing oral health behavior in high school students. Methods: A questionnaire, school oral examination, and oral malodor measurement were conducted on senior high school students in a Tokyo metropolitan school in 2007. A total of 474 students (male: 219, female: 255) were used for the analysis. Results: Over 42% of subjects reported that they had experienced anxiety, or were conscious of oral malodor, on at least 1 occasion. The students who had detectable oral malodor comprised 39.6% of subjects. The binary logistic regression analyses showed that whether or not subjects ate breakfast before the oral examination (p less than 0.05), the presence of plaque (p less than 0.01), and presence of a substantive tongue coating (p less than 0.01) were related to the presence of detectable oral malodor. Conclusions: Cleaning the oral cavity and eating breakfast are important to prevent oral malodor in high school students. This study indicated that school health education incorporating prevention of oral malodor as a motivation tool for oral health promotion could be a valuable procedure to include in high school dental health education programs. (Contains 4 tables.)