Objective: To test the hypothesis that physician assurances of confidentiality influence adolescents' willingness to disclose information and return for future visits by influencing adolescents' trust, comfort, and perceptions of physicians as persons that teens can talk to. Design: A randomized control trial involving 92% of the students in mandatory classes in 3 suburban public high schools in California (N=562) was used to test the hypothesized model. After random assignment to 1 of 3 groups, participants listened to a standardized audiotape depiction of an office visit during which they heard a physician assure unconditional confidentiality, a physician assure conditional confidentiality, or a physician who did not mention confidentiality. Participants then completed an anonymous written questionnaire which contained measures for all model variables. Mediating variables included participants' perception of the scenario-physician as a person that teens can talk to, feel comfortable with, and trust. Outcome variables included participants' willingness to disclose information, intended honesty of disclosure, and likelihood of return visits to the physician depicted in the scenario. The model was tested using ordinary least squares path analysis. Results: Physician assurances of confidentiality decreased adolescents' anxiety and increased adolescents' comfort, general trust, trust regarding discussion of sensitive topics, and perception of the physician in the tape as someone teens can talk to. In turn, these mediating variables increased adolescents' willingness to disclose general information(R2 =.31, p <.001), disclose sensitive information regarding sexuality, substance use, and mental health (R2 =.48, p <.001), intended honesty of disclosure (R2 =.24, p <.001), and likelihood of future visits (R2 =.42, p<.001). Conclusions: Physician assurances of confidentiality increase adolescents' willingness to disclose information and seek health care in part by increasing adolescents' trust, comfort, and perceptions of physicians as persons that teens can talk to.