This study aimed to explore societal determinants of HIV vulnerability among the clients of female commercial sex workers (FCSWs) in Belu and Malaka districts, Indonesia. A qualitative inquiry using in-depth interviews was employed to collect data from participants (n = 42) recruited using a purposive and snowball sampling technique. Data analysis was guided by a qualitative data analysis framework. The study results revealed several societal determinants that supported vulnerability to HIV infection among the participants. They included low education level and sexual health literacy including the lack of knowledge and information about HIV transmission and prevention. Additional determinants identified were limited source of HIV/AIDS-related information, availability of and ease of accessibility of brothels and FCSWs, peer influence, and high mobility of the study participants. Findings of this study indicate the needs and call for interventions that aim to protect both FCSWs and their clients, through provision of HIV/AIDS and sexual health education and information and improvement in the availability and accessibility of condoms.