In four studies, the authors explored the emergence of one-shot illusory correlations--in which a single instance of unuusal behavior by a member of a rare group is sufficient to create an association between group and behavior. In Studies 1, 2, and 3, unusual behaviors committed by members of rare groups were processed differently than other types of behaviors. they received more processing time, prompted more attributional thinking, and were more memorable. In Study 4, the authors obtained evidence from two implicit measures of association that one-shot illusory correlations are generalized to other members of a rare group. The authors contend that one-shot illusory correlations arise because unusual pairings of behaviors and groups uniquely prompt people to entertain group membership as an explanation of the unusual behavior.