The developmental courses of specific temperamental constructs were explored by using structural equation model fitting. Maternal ratings were obtained from either 2 or 3 different temperament questionnaires for 180 children at 3, 6, 12, 18, 24, 36, and 48 months of age. Several formal structural models were fit in infancy (3-18 months), in the toddler-preschooler period (24-48 months), and across all measurement occasions. In infancy, the autoregressive simplex model fit well for all 4 composites considered: Positive Emotionality, Distress-Anger, Fear, and Activity Level. In contrast to the considerable change in temperament during infancy, temperament appears to be very stable from 24 to 48 months of age, and a common factor model fits well with these data. Across all measurement occasions, models that allowed for stability in temperament to be at least partially mediated through intermediate forms of the trait fit best.