This study was conducted with 705 high school students (360 ninth graders and 345 11th graders; 305 female, 400 male) for the purpose of determining their knowledge and attitudes about HIV/AIDS. Data were obtained using a self-completed questionnaire. The questionnaire was divided into three sections. Section A included questions about descriptive characteristics of the students. Section B included questions about HIV/AIDS knowledge. Section C included questions about students' attitudes towards AIDS and their information sources. The percentage, correlation, and one-way analysis of variance were used for data analysis. Research findings showed moderate knowledge levels (59.15 +/- 14.22 out of 100 points) in a sample group of 705 Turkish high school students on all AIDS-related questions. Students in private schools had higher scores than those in public schools; boys had higher scores than girls; 11th graders had higher scores than ninth graders, and the methods of transmission were better known than methods of nontransmission. Scores increased in parallel with student age. Knowledge scores of students were also positively correlated with a higher level of parent education and the ease with which sexuality-related subjects were discussed at home. About half of the students believed that people with HIV/AIDS should be able to attend school and should not have to stop working. Most of the students were informed about HIV/AIDS by media. To prevent the illness, the most important role of the nurses is to focus on education and information for individuals, families, and communities.