Mining communities with migrant populations are high-risk locations for human immunodeficiency virus (HIV)/sexually transmitted infection transmission in Sub-Saharan Africa. Interventions presupposing certain groups to be at high risk, such as those working exclusively as commercial sex workers, may divert attention from other high-risk groups. Qualitative research was conducted in a small town adjacent to a large-scale commercial gold mine in north-western Tanzania. Objectives were to identify populations at high risk of HIV and suggest suitable behavioural interventions by gaining an understanding of sexual behaviour patterns in the town. Rapid assessment procedures were employed comprising participant observation, informal questioning and in-depth interviews. Epidemiological categories of "core", "bridging" and "general" populations may not be adequate to the understanding of risk. Many types of women were found to receive payment for sex, distinguished by permanency of residence, age, relationship status, accommodation and income-earning activity. Paying for sex and having multiple partners was common among most men. The town was a high-risk environment as a result of the economic opportunities available there (in contrast to the poverty of surrounding areas), which were often accessed by offering sex in exchange for money or gifts. In this environment, the potential for spread of HIV infection between sub-populations was high and identification of distinct high- and low-risk groups not possible. However, the methodology enabled the identification of different social circumstances of risk, such as residential arrangements, employment status and venues for recreation, associated with different types of people. Targeted interventions may be oriented to specific circumstances in order to address risk practices in a culturally appropriate manner. It is useful to think of risk environments rather than attributing risk to types of people, and to target interventions to these environments. The methodology also enabled an approach to interventions sensitive to different circumstances associated with risk within the town while identifying structural factors affecting risk at the level of the town as a whole.