Prevalence estimates and prototype perceptions related to health risk behaviors were assessed in comparable samples of Danish and American adolescents (ages 13-15 years). Partly on the basis of observation and previous research, the assumption was made that the American sample would report more self-enhancement tendencies than would the Danish sample. Consistent with this assumption, which was supported by the data, 2 hypotheses were tested: (a) The Americans would overestimate the prevalence of the various risk behaviors (among their peers) more so than would the Danes and (b) those estimates would be more closely linked to their own risk behaviors for the American sample. Results supported both hypotheses; motivational explanations were proposed for both effects. In addition, perceptions of the prototypes associated with particular risk behaviors were assessed and were found to predict smoking behavior and willingness to engage in unprotected sexual intercourse for both samples. Implications for the study of adolescent risk behavior are discussed.