The places where adolescents live, learn, and play are thought to influence behaviours and health, but we have limited tools for measuring environmental risk on a hyperlocal (e.g. neighbourhood) level. Working with 218 adolescents and their parents/guardians in rural western Kenya, we combined participatory mapping activities with satellite imagery to identify adolescent activity spaces and create a novel measure of social-ecological risks. We then examined the associations between social-ecological risk and individual HIV risk beliefs and behaviours. We found support for the conjecture that social-ecological risks may be associated with individual beliefs and behaviours. As social-ecological risk increased for a sample of Kenyan adolescents, so did their reports of riskier sex beliefs and behaviours, as well as unsupervised outings at night. This study reinforces calls for disease prevention approaches that go beyond emphasising individual behaviour change.