Background: High attrition is a major problem for Adolescent Living with HIV (ALHIV) transitioning from pediatric to adult care. Although the HIV Teen Club model has been shown to promote antiretroviral (ARV) adherence and viral suppression among ALHIV, its effect on promoting transitioning ALHIV from pediatric to adult care has not been formally evaluated. We sought to estimate the proportion of ALHIV enrolled in HIV Teen Clubs who successfully transitioned to adult care within six months of the expected transition time and assess health facilities’ fidelity in implementing HIV Teen Clubs’ adult care transition protocols and factors associated with successful transition to adult Care. Methods: From September 2018 to June 2019, we conducted a retrospective cohort study involving ALHIV attending HIV Teen Clubs in 14 primary health facilities in Blantyre, Malawi who had reached the recommended transition age of 18/19 years between July - December 2017. After obtaining consent, we reviewed their records to assess the proportion who successfully transitioned and also factors associated with transitioning. Checklist was used to ascertain fidelity of implementation of HIV Teen Club transition protocols. In-depth interviews were conducted with service providers (SP) in health facilities providing HIV Teen Club to get their perspectives on reasons for successful or unsuccessful transition.Results: Of the 131 eligible ALHIV enrolled in the study, only 6.9% (n=9) successfully transitioned to adult care within six months of the expected transition time. The overall fidelity in implementing adult care transition protocols in health facilities was medium. There was an association between implementation fidelity and ALHIV successful transition with 2 out of 3 health facilities with high implementation fidelity also successfully transitioning ALHIV into adult care. Successful ALHIV transitioning was associated with urban location of health facilities and ownership of the facilities by NGOs. SPs reported that lack of training in transitioning ALHIV, lack of clear guidelines, inadequate human resource and refusal of ALHIV to transition were some of the health system factors negatively influencing successful transition. Conclusions: Training and mentorship of SP in implementing transitioning protocols and adequately resourcing HIV teen clubs may improve their operations and facilitate successful transitioning.