Performance-based incentives may improve the validity of results from implicit attitude assessment tasks and improve attrition rates. Participants working to obtain the incentive may be less likely to edit their responses to conform to social expectations and more likely to meet experimental inclusion criteria. We examined the influences of a monetary incentive ($20 voucher) for fast and accurate performance on an Implicit Relational Assessment Procedure (IRAP) task evaluating implicit attitudes about bodyweight. We randomly assigned 82 university students to incentive and control (non-incentive) groups. Although there was no significant effect on accuracy or latency measures, participants in the incentive group displayed a significantly stronger bias against overweight individuals than did participants in the control group. There were no differences between groups with respect to attitudes toward slim individuals. More participants in the incentive group (97.5%) met performance criteria than in the control group (87.8%). These results suggest that incentives for meeting performance criteria may reduce the attrition rate and increase the validity of the IRAP and other implicit measures, but additional research is required to determine the predictive validity of implicit attitude assessments with and without performance-based incentives.