Adolescence is a critical age in which people undergo sexual development, unfortunately, it is also a period when many uninformed and unsafe practices in terms of sexual behaviour are committed by young persons. Different studies have established that adolescents are slightly at an increased level of vulnerability for different health conditions including sexually transmitted diseases when compared to adult population, such as those between ages 45 – 60 years. The aim of this paper was to investigate how the sexual behaviour of youths contributes to the spread of HIV/AIDS in Nigeria, using Okirika Local Government Areas as a case study. The study relied on a cross-sectional survey method and a conveniently selected sample of 399. Data collected with questionnaires were analysed using simple percentages and charts. Findings show that whereas there is a high awareness of HIV/AIDs among young persons in Okrika LGA, many adolescents still engage in different risky sexual behaviour that expose them to risk of contracting HIV/AIDs. Part of the factors that encourage risky sexual behaviour as found in the study includes: poor family background, household size and presence of parents, social media, and music/videos as found in the entertainment industry. Many respondents also indicated that peer pressure is a major concern in the phenomenon of risky sexual behaviour among adolescents. These findings can be explained using the theory of Differential Association whose main assumption is that deviant behaviour is rooted in social organization and the nature of association people have.