Although prosocial behavior has been moving in directions that highlight complexity over the past few years, little research has assessed the cost of this behavior. This study created a scale assessing the tendency to perceive costs of prosocial behavior. This was validated via focus groups, content and discriminant validity. In six focus groups, 29 13- to 25-year olds described specific prosocial acts and the costs that they experienced from the act. A questionnaire was then given to 391 emerging adults. Exploratory and confirmatory factor analyses were conducted. Results suggest a four-factor solution with adequate model fit, suggesting cognitive, behavioral, emotional, and social costs. Convergent and discriminant validity add support to the scale. Discussion focuses on the implications of this measure for the prosocial behavior literature and important future directions.