Most adults can easily distinguish between stable characteristics, which affect personal identity, and changeable ones, which are free to vary within an individual. The purpose of this study was to investigate preschoolers' developing knowledge of stable (identity, gender, and race), changeable (mood, weight, and health), and changeable-but-irreversible (age and height) characteristics using pictorial and question tasks. In the first two experiments, 3-, 4-, and 5-year-old children and adults were asked to judge whether two pictures could represent the same person. Children in these experiments understood stable properties more clearly than changeable or irreversible ones. Children who made mistakes tended to treat changes in variable characteristics as if they altered personal identity. In Experiment 3, subjects answered questions about the stability or variability of the same characteristics. Children tested with questions in Experiment 3 showed a better understanding of stable and variable characteristics than did children tested with pictures in Experiments 1 and 2. Most of the children who erred in Experiment 3 understood stable attributes but treated changeable ones as if they were constant; however, a minority of children understood changeable properties but treated stable ones as if they were variable. These findings provide new information about how children understand and misunderstand the status of personal attributes.