In this study the relationship between temperament and development in preschool children was determined. Thirty-one children, age 3 and 4 years old, were selected from day-care centers. The child's temperament was measured with the Behavioral Style Questionnaire. Cognitive-verbal and motor development were assessed using the Pea-body Picture Vocabulary Test, the Goodenough Draw-a-Person Test, and the developmental subtests of the Comprehensive Identification Process. Significant correlations (p < .05) using the Pearson product moment were found between development and six categories of reactivity for temperament: activity, rhythmicity, approach, adaptability, mood, and persistence. All significant correlation coefficients showed an inverse relationship between temperament and developmental scores. This suggests that children who are mildly active, rhythmic, adaptable, persistent, approachable, and have a positive mood attain a more advanced developmental level during their preschool years.