This paper describes a revised measure of self-efficacy to overcome barriers to moderate and vigorous physical activity in a sample of 484 high school students in Toronto, Ontario. The students had a mean age of 15.3 years. Principal axis factoring with oblique rotation yielded five factors: self-efficacy to overcome internal, harassment, physical environment, social environment, and responsibilities barriers. Two problematic items were removed, which resulted in a 22-item measure. Subsequent analyses were conducted on responses to this shortened measure. Confirmatory factor analysis supported the five-factor model and demonstrated age- and sex-invariance. The subscales had good internal consistency reliability. Structural regressions demonstrated a strong relationship between the resulting factors and a physical activity measure (energy expenditure), showing predictive validity. (Contains 2 tables and 1 figure.)