Objective: The main objective of this study was to determine the ability of high school students to critically evaluate health claims as well as their attitudes and behaviors regarding health decision making. The specific objectives of the study were to assess whether there is a difference in the ability to assess health claims with respect to the gender of the respondents and to examine differences in the assessment of health claims with respect to the different high school programs that respondents attend. Materials and methods: 302 high school students from Split-Dalmatia County participated in this research, but 13 students did not complete the questionnaire, so a total of 289 questionnaires were analyzed. For the purposes of this research, we used a test composed of validated questions compiled as part of a project called Informed Health Choices, which are available in the database of so-called questions. CLAIM Evaluation Tools Database. The questionnaire was completely anonymous and consisted of 18 questions in which students were required to demonstrate the ability to assess the health claims offered. The data were processed in Microsoft Excel 2007 and coded for further statistical processing. The data were anzlysed by using the SPSS statistical software (IBM Corp., Armonk, New York). Results: When it comes to knowledge and attitudes about health claims, statistical analysis found a difference in the number of correct and incorrect answers. Three students had only three correct answers, which is also the worst result of the questionnaire. No student had all 18 correct answers, and the best solved test with 17 correct answers. With regard to the gender of the respondents, the second hypothesis was rejected and therefore further analyzes for male and female sex were done separately. It is noticed that the female students answered exactly 11.43 questions on average, while the male students answered 10.33 questions correctly. No differences were observed between grammar schools and health schools (p = 0.25). No differences were found in the results of the questionnaire among students with regard to the type of school, but there is a noticeable tendency towards a difference (P <0.10). Subsequent, the so-called post-hoc analysis using the LSD Fisher test, however, found that there was a significant difference between students attending vocational schools and high school students (p = 0.032). Conclusion: Students' overall knowledge of health claims is varied. A statistically significant difference in knowledge between males and females was observed. Also, within the subsample of respondents there is a difference depending on the type of school they attend. This research could serve as an incentive for students to develop better skills in seeking and assessing the accuracy of health data and claims. Future research should take into account several variables, such as the high school health programs being conducted, the amount of literature the student reads, the level of parental education, and try to analyze the researched critical judgment skills against these variables.