Evidence-based interventions (EBIs) are used in public health to prevent HIV infection among youth and other groups. EBIs include core elements, features that are thought to be responsible for the efficacy of interventions. The authors evaluate experiences of organizations that adopted an HIV-prevention EBI, Focus on Kids (FOK), and their fidelity to the intervention's eight core elements. A cross-sectional telephone survey was administered to 34 staff members from organizations that had previously implemented FOK. Questions assessed how the organization adhered to, adapted, dropped, or altered the intervention. None of the organizations implemented all eight core elements. This study underscores the importance for HIV intervention researchers to clearly identify and describe core elements. More effort is needed to reflect the constraints practitioners face in nonresearch settings. To ensure intervention effectiveness, additional research and technical assistance are needed to help organizations implement HIV prevention EBIs with fidelity. (Contains 3 tables.)