Despite a growing awareness of HIV and AIDS, the outbreak of the disease continues unabated, disproportionately hurting the young. The Internet is a potentially powerful medium for delivering quality HIV education to youth. However, it may also serve as a medium of misinformation and deception. While a number of studies have documented that adolescents have a basic mastery of AIDS" facts", few studies have evaluated youth's in-depth understanding of the underlying concepts, let alone its application. Meanwhile, cognitive studies of lay understanding of health and disease suggest that this understanding is fragmented and opportunistic, lacks conceptual cohesiveness, and incorporates a mix of medical facts, cultural beliefs, social norms and personal experience. Studies of lay understanding of health and disease suggest that adolescents may lack conceptual knowledge, essential for evaluating the quality ofweb information about HIV. The present study addresses two questions. First, what is the nature of adolescent knowledge about HIV? Second, how do adolescents apply this knowledge when evaluating information? Answering these questions could provide important insights about the potential strengths and pitfalls of HIV education via Internet.