Worldwide, adolescents are exposed to an array of challenges that include unplanned pregnancies, sexually transmitted infections (STIs) and Human Immunodeficiency Virus (HIV). In South Africa, UNAIDS (2019) estimates that 69,000 female and 25,000 male adolescents acquired HIV in 2018. Little research has investigated the role of the family in influencing adolescent sexual behaviour. The significance of selecting South Africa, particularly Cape Town in the province of Western Cape to highlight the family environment and adolescent sexual behaviour nexus was done due to the historical background of high inflow of local and international migration to the city. By far, Western Cape’s HIV prevalence rate of 8.9% in a hyperendemic South African context, makes it one of the lowest in the country (Simbayi et al., 2019). Nevertheless, attractive economic prospects particularly in the city of Cape Town is likely to attract both international and local immigration which is likely to trigger an upward trend of HIV infections. Guided by the Life-Course Perspective Theory, this mixed method approach was carried out firstly, to understand the link between the family structure, the family’s financial circumstances, and parental engagement with their children and adolescent sexual behaviour; and secondly, to understand the perceptions of adolescents and parents on the role played by the family environment in shaping sexual behaviour among adolescents. The study drew data from the Cape Area Panel Study (CAPS); a longitudinal study conducted in Cape Town. The study tracked the lives of 4,752 adolescents aged between 14 and 22 and the study spanned between 2002 and 2009. In addition, 15 in-depth interviews (IDI) with adolescents and three (3) focus group discussions (FGD) with parents and adolescents were conducted. The participants in the IDI and FGD were recruited from the same sampling clusters as CAPS. The panel data were analysed using the logistic regression analysis reporting odds ratios (OR), and qualitative data using thematic analysis and the NVivo 11. Adolescents aged between 16 and 19 had higher odds of reporting having initiated sex and having experienced a pregnancy compared to adolescents aged between 14 and 15 years. Odds of reporting early sexual debut and adolescent pregnancy were lower among adolescents living in a family with a father, respectively. Adolescents from a family with a monthly income = R25, 001 had less odds of having experienced a pregnancy, and higher odds of reporting condom use among adolescents from families with an income of R25, 001 and above compared to adolescents from a family with an income of R5,000 and less. These results were later supported by results from the qualitative data as both parents and adolescents blamed early sexual debut and pregnancy on the family environment. The study confirms the important role played by the family environment in determining adolescent sexual behaviour. It recommends the need to pay attention to families when designing sexual and reproductive health (SRH) programmes for adolescents.