Participants were 848 adolescents (377 males and 469 females, 2 unknowns) between 14 and 18 years old, who were students in high schools in Seattle, WA; Portland, OR; and Los Angeles, CA. In the fall of 1999 and spring of 2000, data were collected in one high-achieving school in each of the three cities. A survey entitled Young People and the Environment was used to measure attitudes, knowledge, goals, self-efficacy, and behaviors relative to the environment. Environmental attitudes were assessed with an early version of the New Environmental Paradigm, and self-efficacy was assessed with a single 10-item scale. Researchers hypothesized that adolescents who showed higher levels of proenvironmental attitudes would engage in more proenvironmental behaviors compared to those adolescents who had lower proenvironmental attitudes. Controlling for gender, this hypothesis was supported. A second hypothesis predicted that adolescents who had high proenvironmental attitudes and high perceived self-efficacy would have greater proenvironmental behaviors compared to adolescents who had low proenvironmental attitudes and low perceived self-efficacy. Controlling for gender difference, findings indicated that perceived self-efficacy was not a significant moderator of environmental attitudes when predicting proenvironmental behaviors. Still, self-efficacy was significantly and positively related to environmental behaviors. Controlling for gender, analyses also showed that environmental knowledge was a significant moderating variable when predicting adolescent proenvironmental behaviors. Environmental knowledge had a greater moderating effect for females compared to males. 6 tables, 3 figures, and 38 references