HIV is a member of the group of viruses known as retroviruses which is enveloped. Recent times have witnessed a transition in the prognosis of Human Immunodeficiency Virus infection from a fatal disease to a chronic manageable disease. HIV infected adolescents face unique challenges when it comes to accepting and treating their diseases. Many adolescents are in denial, afraid, misinformed or lack familial or social support. Therefore, this age group may benefit from counselling services and supportive care. Adolescent HIV/AIDS is an epidemic with difference and its control needs to be adolescent specific. Aim :This study was carried out to assess the knowledge regarding HIV/AIDS among adolescents studying in a senior secondary school. Setting and Design :Government Model Senior Secondary School, Sector-10, Chandigarh was used to collect relevant data. Quantitative research approach and a descriptive research design was used for the study. Material and Methods : The study was conducted on a sample of 100 students of age group 16-20 yrs. were selected from Government Model Senior Secondary School using simple random sampling. Data was collected using self structured multiple choice questionnaire on HIV/AIDS. The collected data was organized, tabulated, analyzed and interpreted using descriptive and inferential statistics. Results :The findings of the study revealed that out of 100 students 91% had average knowledge followed by 6% who had poor knowledge and 3% had good knowledge. There was no significant association of knowledge regarding HIV/AIDS among adolescents studying with socio-demographic characteristics. After the completion of study, health education was imparted to the students regarding prevention of HIV/AIDS.