Purpose: The purpose was to develop a preliminary scale to measure Korean adolescents' health behaviors through a qualitative approach, to evaluate the scale psychometrically, and to develop a final scale. Methods: Participants were 61 adolescents for qualitative interviews and 1,687 adolescents for the psychometric evaluation. Procedure included content analysis of interviews to identify health behavior categories for Korean adolescents, pre-test to confirm that preliminary scale items were understandable, content validity by an expert panel, development of the web-based computer-assisted survey (CAS), and psychometric analysis to determine reliability and validity of the final scale. Results: A final scale was developed for both paper-and-pencil and CAS. It consisted of 14 health behaviors (72 items), including stress and mental health (10), sleep habits (5), dietary habits (12), weight control (4), physical activity (4), hygiene habits (5), tobacco use (5), substance use (2), alcohol consumption (4), safety (4), sexual behavior (9), computer use (3), health screening (4), and posture (1). Conclusion: The scale's strong points are: 1) Two thirds of the final scale items are Likert scale items, enabling calculation of a health behavior score. 2) The scale is appropriate to Korean culture. 3) The scale focuses on concrete health behaviors, not abstract concepts.