The global epidemic of Human Immunodeficiency Virus/Acquired Immune Deficiency Syndrome (HIV/AIDS) has affected all countries, including the Philippines. Prevention is seen as the only hope for steaming the epidemic. This study aimed to investigate the effect of a psychoeducational intervention on the knowledge about the and attitude toward HIV/AIDS and its prevention among adolescents. This experiment, which used the pre-test posttest control design, was conducted in February 1997 among the 30 randomly selected freshmen students at the WVSU Institute of Mass Communication, who were further divided into the experimental and the control groups. Data for the investigation were gathered through the used of a checklist on HIV/AIDS awareness, adopted from one developed by the Philippine HIV/AIDS NGO Support Program (PHANSUP). Descriptive statistics employed were means and standard deviations. Inferential statistics used were the t-test for independent and nonindependent samples and the Pearson's r set at .05 alpha level. Findings showed that, generally the experimental and control subjects manifested high level of knowledge about HIV/AIDS and its prevention in the pre- and posttest stages. Both groups also showed neutral pre-intervention attitude toward HIV/AIDS and its prevention. However, while the experimental group's post-intervention attitude was positive, the control subjects' post-intervention attitude remained neutral. The experimental subjects differed significantly in their post-intervention attitude grouped as as to school type in favor of those from private high schools. Significant differences existed between the experimental and control subjects' pre-intervention knowledge about and attitude toward HIV/AIDS and its prevention.The experimental subjects' pre and post-intervention knowledge and attitude differed significantly in favor of the posttest. The control subjects' pre and post intervention knowledge about and attitude toward HIV/AIDS and its prevention differed significantly which generally flavored the pre-test. The experimental subjects' pre-intervention attitude toward HIV/AIDS and its prevention was positively and significantly associated with their post-intervention attitude. On the other hand, the control subjects' pre and post intervention knowledge was positively associated but were negatively but significantly associated with their post-intervention attitude toward HIV/AIDS and its prevention.