In the life cycle of a Homosapiens, adolescence is a period of transition from childhood to adulthood. It is characterized by rapid physical, biological and hormonal changes resulting in to psychosocial, behavioral and sexual maturation between the ages of 10-19 years in an individual. Adolescence is often described as a phase of life that begins in biology and ends in society. It means that physical and biological changes are universal and take place due to maturation but the psychosocial and behavioral manifestations are determined by the meaning given to these changes within a cultural system. The experience of adolescents during teen years would vary considerably according to the cultural and social values of the network of social identities they grow in. (ADOLESCENT IN INDIA: PROFILE 2003) The problems of adolescents are multi-dimensional in nature and require holistic approach. A large number of adolescents in India are out of school, malnourished, get married early, are working in vulnerable situations and are sexually active. They are exposed to tobacco or alcohol abuse. This writing makes an attempt to find the answer to the question; What is the level of knowledge, and attitude of adolescent boys aged 10-19 years in relation to HIV/AIDS in Jannat nagar (Urban Slum)?This writing is based on both the primary and secondary data. Key Words:Adolescence, Knowledge and Attitude, HIV/AIDS.