There is an urgent need to develop positive prevention interventions for adolescents living with HIV in high endemic regions. Adapting existing evidence-based interventions for resource-constrained settings is effective when the intervention's theoretical core elements are preserved while achieving cultural relevance. We describe the process of adapting a primary prevention to a secondary/positive prevention programme for adolescents living with HIV in Kenya and Uganda. The systematic adaptation was guided by the Centers for Diseases Control's map for the adaptation process, describing an iterative process. The procedure included: assessing the target positive prevention group's needs (safer sex; fertility-related issues), identifying the potential interventions through a literature review, conducting qualitative adaptation research to identify areas for adaptation by ensuring cultural relevance (revising the intervention logic by adding topics such as adherence; HIV-related stigma; HIV-disclosure; safer sex), pilot-testing the adapted programme and conducting a process evaluation of its first implementation. Areas added onto the original intervention's logic framework, based on social cognitive theory, the theories of reasoned action and planned behaviour were information and skills building on sexual relationships and protection behaviour, prevention of vertical HIV transmission, contraception, HIV-disclosure, HIV-related stigma, HIV-treatment and adherence. The process evaluation using mixed methods showed that we delivered a feasible and acceptable intervention for HIV-positive adolescents aged 13-17 years. The systematic approach adopted facilitated the development of a contextualized and developmentally appropriate (i.e. age-specific) intervention for adolescents living with HIV.