BACKGROUND: HIV remains a leading contributor to the disease burden in sub-Saharan Africa, with adolescents and young people disproportionately affected. Optimising pre-exposure prophylaxis (PrEP) uptake has predominantly focused on women and adult men who have sex with men. We explore adolescent boys and young men's PrEP uptake preferences in South Africa, Uganda, and Zimbabwe. METHODS: A cross-sectional sequential exploratory mixed-methods study amongst males aged 13-24 years was conducted between April and September 2019 as part of the CHAPS trial. Group discussions (GDs) and In-Depth Interviews (IDIs) focused on motivations and hindrances for HIV testing, PrEP preference, and reasons for the uptake of PrEP. A thematic approach was used to analyse the qualitative data. A quantitative survey following the qualitative work covered questions on demographics, HIV risk and PrEP preferences (on-demand vs. daily). For quantitative analysis, we fitted logistic regression models to determine factors associated with on-demand vs daily PrEP preference. RESULTS: Overall, 647 adolescent boys and young men (median age 20, IQR: 17-22) were enrolled. Of these, 422 (65.22%) preferred on-demand PrEP (South Africa 45.45%, Uganda 76.80%, Zimbabwe 70.35%; p<0.001). Factors independently associated with on-demand PrEP included country (South Africa, adjusted odds ratio (aOR) = 0.19 [95%CI:0.1-0.3] compared to Uganda) and advanced planning of sex [>24 hours in advance aOR = 1.4 (0.9-2.3) compared to <2 hours]. Qualitatively, participants commonly believed they were not at risk of HIV acquisition most of the time and thought that on-demand PrEP would be suitable as they tend to plan sexual activity in advance. CONCLUSION: Preference for on-demand PrEP is high in young males. The qualitative data support a preference for on-demand PrEP in those who plan sex in advance. HIV intervention programs should offer both on-demand and daily PrEP to engage more adolescent boys and young men in HIV prevention practices.