A growing body of evidence focuses on the experiences of young men in low-income countries, including their health vulnerabilities. Much of this research has been conducted in sub-Saharan Africa, Asia and Latin America. Limited evidence exists on the norms influencing boys' transitions into young adulthood in Southeast Asia, and in Cambodia in particular. To help fill this gap, we conducted a comparative case study using participatory methods with 16-19-year-old young men in rural and urban Cambodia, and with the adults who intersect in their lives. Findings suggest that in line with their counterparts growing up elsewhere, Cambodian boys welcome becoming young men as a time of newly acquired adult roles and responsibilities, while some may experience growing up as a time of bodily change, burgeoning sexual feelings and limited sources of support and guidance. As a result, some may strive more intensely to conform to the alcohol use and violence modelled by the older men in their environments. Additional research is needed to better understand the vulnerabilities of boys' transition into young adulthood in Cambodia today, and how to prevent or reduce engagement with these more negative practices.