Background: Individuals with Williams syndrome (WS) are reported to display increased sociability towards strangers, leading to increased social vulnerability. No research has examined real life interactions of adults with WS towards strangers and no interventions have been implemented to teach stranger safety skills to this population. Method: Twenty-one adults with WS participated in 3 days of behaviour skills training to learn how to respond to a stranger lure. Skill acquisition was assessed "in situ"; confederate strangers approached participants, presented a lure and recorded the participants' response. Results: Prior to intervention, 14% of participants walked away from a stranger. Participants were able to accurately use the skills in role play. After training, 62% of participants said "no" and walked away and only 14% agreed to leave with the stranger during "in situ" assessments. Conclusions: Individuals with WS are at-risk but can learn how to appropriately respond to lures from strangers. Further research is needed to increase use of safety skills in various conditions.