The purpose of this study was to demonstrate construct validity for the Ego State Questionnaire (ESQ) using factor analysis. The ESQ is a 40-item experimenter-constructed instrument that measures the strength of functional ego states. Two hundred students were asked to complete the ESQ in class. A VARIMAX rotation factor analysis of the 200 Ego State Questionnaires revealed five primary factors corresponding to the five functional ego states. Thus, factor analysis of the ESQ revealed that it does measure five functional ego states (factors), although with varying accuracy.