This study investigated whether the risk taking behaviour of others signals shared group membership. 89 participants were randomly assigned to experience one of three experimental conditions, designed to manipulate the observed risk taking behaviour of another, unknown individual. These manipulations were operationalised to reflect health risk taking through perceived drink sharing with a confederate. Depending on experimental condition, confederates displayed either risk avoidance or risk acceptance behaviour. A control condition was also employed, presenting no opportunity for risk taking. Through insights gained from previous research, it was predicted that participants who witnessed the risk acceptance manipulation would perceive greater social affiliation with the confederate. It was also expected that this relationship would be mediated by increased trust inferred to be felt by the confederate. Results supported these predictions, providing support for an indirect effect of risk taking on affiliation, via increased trust. Various theoretical and practical implications are discussed in relation to these findings, along with suggestions for related future research.