The authors compared parents' perceptions of their college student children's health and health risk behaviors with the college students' own reports. One hundred sixty-four parent-college student child dyads completed questionnaires regarding the students' health, illness status, and health risk behaviors. Parents tended to be overoptimistic about their children's health and health risk behaviors, underestimating the frequency of their children's alcohol, smoking, marijuana, and sex-related behaviors, and overestimating the students' self-reports of general health. Such misperceptions may inhibit parent-student conversations about health and risky health behavior, ultimately putting the student at greater health risk. (Contains 1 note.)