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 stemming the epidemic.This study aimed to investigate the effect of a psychoeducational intervention on the knowledge about and attitude toward HIV/AIDS and its prevention among adolescents. This experiment, which used the pretest post test control design, was conducted in February 1997 among the 30 randomly selected freshmen students at the WVSU Institute of Mass Communications, who were further divided into the experimental and the control groups.Data for the investigation were gathered through the use of a checklist on 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 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 pretest post test 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 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 post test. The control subjects' pre- and post- intervention knowledge about and attitude toward HIV/AIDS and its prevention differed significantly which generally favored 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 towardHIV/AIDS and its prevention.