The focus of the article is the validation of an instrument to assess gifted students' affect after mathematical problem solving tasks. Participants were 225 students identified by their district as gifted in grades four to six. The Chamberlin Affective Instrument for Mathematical Problem Solving was used to assess feelings, emotions, and dispositions after students solved model-eliciting activities in groups of three. Through the use of principal component analysis, it was determined that three factors should be retained. The instrument holds promise because it may be used to assess affect, which has implications for identification and curricular adjustments to optimize affect. (Contains 1 table and 1 figure.)