Advances in technology have led to development of new vaccines for adolescents, but these vaccines will be added to a crowded schedule of recommended adolescent clinical preventive services. We reviewed adolescent clinical preventive health care guidelines and patterns of adolescent clinical preventive service delivery and assessed how new adolescent vaccines might affect health care visits and the delivery of other clinical preventive services. Our analysis suggests that new adolescent immunization recommendations are likely to improve adolescent health, both as a "needle" and a "hook." As a needle, the immunization will enhance an adolescent's health by preventing vaccine-preventable diseases during adolescence and adulthood. It also will likely be a hook to bring adolescents (and their parents) into the clinic for adolescent health care visits, during which other clinical preventive services can be provided. We also speculate that new adolescent immunization recommendations might increase the proportion and quality of other clinical preventive services delivered during health care visits. The factor most likely to diminish the positive influence of immunizations on delivery of other clinical preventive services is the additional visit time required for vaccine counseling and administration. Immunizations may "crowd out" delivery of other clinical preventive services during visits or reduce the quality of the clinical preventive service delivery. Complementary strategies to mitigate these effects might include prioritizing clinical preventive services with a strong evidence base for effectiveness, spreading clinical preventive services out over several visits, and withholding selected clinical preventive services during a visit if the prevention activity is effectively covered at the community level. Studies are needed to evaluate the effect of new immunizations on adolescent preventive health care visits, delivery of clinical preventive services, and health outcomes.