Adolescent diets may be influenced by the retail food environment around schools. However, international research to examine associations between the proximity of retail food outlets to schools and diet provides equivocal support for an association. This study aims to understand the school food environment and drivers for adolescents' consumption of unhealthy foods in Addis Ababa, Ethiopia. Mixed-methods research was conducted, 1200 adolescents (10-14 years) from randomly selected government schools were surveyed, along with vendors within 5-min' walk of the schools and focus group discussions (FGDs) with adolescent groups. Mixed-effect logistic regression investigated the relationship between the number of vendors around the schools and the consumption of selected unhealthy foods. Thematic analysis was used to summarize findings from the FGDs. Consumption of sweets and sugar-sweetened beverages (S-SSB) and deep-fried foods (DFF) at least once a week was reported by 78.6% and 54.3% of the adolescents, respectively. Although all schools were surrounded by food vendors selling DFF and S-SSB, consumption was not associated with the number of vendors available around the school. However, adolescents' awareness and perception of healthy food, and their concerns about the safety of foods in the market, influenced their dietary choices and behaviours. Lack of financial resources to purchase food as desired also played a role in their selection of food and eating habits. Reported unhealthy food consumption is high among adolescents in Addis Ababa. Thus, further research is warranted to come up with school-based interventions that promote access and healthy food choices among adolescents.