To identify the psychosocial factors associated with voluntary cooperation in mass genetic testing, stratified random samples of 500 participants and 500 nonparticipants were drawn from an identified at-risk population for Tay-Sachs disease. Participants were relatively younger and better educated, reported higher levels of perceived susceptibility to being a carrier, and also stated more often that the impact of learning of being a carrier would be low. Participants were also more likely to indicate they would not alter plans for future progeny. Recommendations are made for enhancing participation in future genetic screening programs of this type.