['The possibility that smoking prevalence among junior and senior high school students may decrease with increasing mobile phone bill was reported by the mass media in Japan. We conducted a nationwide survey on adolescent smoking and mobile phone use in Japan in order to assess the hypothesis that mobile phone use has replaced smoking.', 'A total of 70 junior high schools (response rate; 71%), and 69 high schools (90%) from all over Japan responded to 2005 survey. Students in the responding schools were asked to fill out an anonymous questionnaire about smoking behavior, mobile phone bill, and pocket money. Questionnaires were collected from 32,615 junior high school students and 48,707 senior high school students.', 'The smoking prevalence of students with high mobile phone bill was more likely to be high, and that of students who used mobile phones costing 10,000 yen and over per month was especially high. When "quitters" were defined as students who had tried smoking but were not smoking at the time of survey, the proportion of quitters decreased as the mobile phone bill increased. The proportion of students who had smoking friends increased with the increase in the mobile phone bill per month.'] Does mobile phone use discourage adolescent smoking in Japan?