This chapter reports partial results of an extensive research project called Health-Enhancing and Health-Threatening Behaviour: Determinants, Models, and Consequences. Its goal is to create models of health-promoting and health-threatening behavior applicable among the Czech population. This is made possible by means of a cross-section research study carried out using sample groups of adolescents, young, middle and advanced aged adults as well as seniors. The presented results focus on the explored selected factors of health-promoting behavior in adolescents, the level of commitment that adolescents invest in taking care of their health, and their cognitive evaluations and perceptions of their own health. In addition, the role of personality characteristics in relation to maintenance, loss or restoration of one‘s health was also explored. The data from the following instruments were utilized in this study: Health-Related Behavior Scale (Dosedlová, Slováčková, & Klimusová, 2013); Subjective Health Problems Inventory (modified version of the inventory by Osecká, Řehulková, & Macek., 1998), and the Big Five Inventory (John, Donahue, & Kentle, 1991). The sample consisted of 835 adolescents (47.4% female) aged 12-19 years. A principal component analysis of the items of the Health-Related Behavior Scale yielded five factors: healthy eating habits, exercise and lifestyle, avoidance of addictive substances and other risks, regular daily routine and emotional well-being. To predict subjective health issues, we used a hierarchical regression analysis with demographic variables entered in the first block, personality factor scores entered in the second block, and health-related behaviors entered in the third block. The results indicated that girls scored higher on the subjective health issues scale; among personality characteristics, higher neuroticism and lower conscientiousness predicted more subjective health issues.