Background: Little is known about the circumstances that prompt teenagers to request emergency contraception (EC). This evaluation was designed to refine the EC clinical protocol and improve pregnancy prevention efforts in high school-based clinics by analyzing information on EC use and subsequent contraception use of EC patients. Methods: Sites included 5 clinics located at mainstream, racially diverse, and urban high schools. Nursing staff documented all EC-related visits during the 2002-2003 school year on a standardized form. These forms and additional information were collected from chart reviews. Results: EC was requested in 113 instances involving 91 students and dispensed in all but 4 instances. The most frequently reported circumstance prompting an EC request was the use of no protection (37.2%), followed by a condom mishap (27.4%) and questionable protection from a hormonal method (23.9%). Anxiety despite adequate protection from a hormonal method (9.7%) or a condom (1.8%) accounted for the remaining cases. Although the clinical protocol included a follow-up appointment 2 weeks after receipt of EC, 39.5% of EC users failed to keep this appointment. The chart review revealed that hormonal contraception was eventually initiated following two thirds (68.0%) of the EC instances that involved either no protection or only a condom. Conclusions: Because young EC seekers vary considerably in terms of sexual experience, contraceptive use consistency, and pregnancy risk, individualized risk assessment and counseling are essential. The EC visit may be an optimal time to encourage initiation or reinstitution of hormonal methods of birth control. (Contains 3 tables.)