ABSTRACT Much of the research and thinking in the area of childhood temperament has been guided by the structural and measurement model of Thomas, Chess, and colleagues. Recently, researchers have called into question this structural conception and have explored the factor structure of the instruments based on the Thomas and Chess model. A review of the literature indicates that there are few studies at any one age level, and that much of the research is limited by small samples. The results of a large sample factor analysis of parent and teacher ratings of preschool children are reported. A five-factor solution was judged most appropriate for parent ratings, and a three-factor solution seemed most appropriate for teacher ratings. Relations of these factors to the Big Five personality factors found in adult personality research are discussed.