Health literacy has come to play a critical role in health education and promotion, yet it is poorly understood in adolescents and few measurement tools exist. Standardized instruments to measure health literacy in adults assume it to be a derivative of general literacy. This paper reports on the development and the early-stage validation of a health literacy tool for high school students that measured skills to understand and evaluate health information. A systematic process was used to develop, score and validate items. Questionnaire data were collected from 275, primarily 10th grade students in three secondary schools in Vancouver, Canada that reflected variation in demographic profile. Forty-eight percent were male, and 69.1% spoke a language other than English. Bivariate correlations between background variables and the domain and overall health literacy scores were calculated. A regression model was developed using 15 explanatory variables. The R(2) value was 0.567. Key findings were that lower scores were achieved by males, students speaking a second language other than English, those who immigrated to Canada at a later age and those who skipped school more often. Unlike in general literacy where the family factors of mother's education and family affluence both played significant roles, these two factors failed to predict the health literacy of our school-aged sample. The most significant contributions of this work include the creation of an instrument for measuring adolescent health literacy and further emphasizing the distinction between health literacy and general literacy.