To identify the sociodemographic and Health Belief Model predictors of follow-up appointment-keeping behavior. Prospective observational study. General adolescent medical clinic. Sequential sample of 166 adolescents (aged 12 to 20 years, mean = 15.9 years) enrolled in the clinic. The population was 75% female; the racial-ethnic distribution of the sample was 37.9% black, 29.8% white, 11.2% Asian, 14.3% Hispanic, and 6.8% "other" background. Subjects' social class was primarily lower-middle (60.5%) and middle class (28.6%). A subsample was randomly assigned to be interviewed about their beliefs concerning their follow-up appointment and the constructs of the Health Belief Model. Forty-eight percent of the total sample failed to keep their follow-up appointment. There was a significant positive correlation between social class and appointment keeping (F = 5.07; df = 5,110; P = .026). Neither race-ethnicity nor who made the appointment were found to be associated with follow-up appointment-keeping. The only construct of the Health Belief Model found to be significantly associated with appointment keeping was the number of potential negative outcomes resulting from noncompliance perceived by the subject (F = 6.85; df = 1.74; P = .011). Clinicians must work with adolescents to improve their understanding of the potential negative outcomes associated with noncompliance to improve appointment-keeping behavior.