This article describes the development, reliability, and factor structure of a finely differentiated (18 dimensions) parent-report measure of temperament in 1.5 to 3-year-old children, using a crosssectional sample (N = 317) and a longitudinal sample of primary (N = 104) and secondary (N = 61) caregivers. Adequate internal consistency was demonstrated for all scales and moderate interrater reliability was evident for most scales. Longitudinal stability correlations were primarily large over 6-and 12-month spans and moderate to large from 18 to 36 months. Factor analysis revealed a three-factor structure of Surgency/Extraversion, Negative Affectivity, and Effortful Control. In both samples and for both primary and secondary caregivers, older children received higher scores for Attention Focusing, Discomfort, Inhibitory Control, and Positive Anticipation. Primary caregivers rated females higher in Fear, and lower in High-intensity Pleasure, than males; secondary caregivers rated females higher than males in several aspects of Effortful Control.Increases in the number of empirical studies of temperament in recent years (Rothbart & Bates, 1998, in press) have been matched by an expanded and more finely defined list of dimensions considered within the temperament realm. Although fine-grained instruments have been developed to assess temperament in infants (Gartstein & Rothbart, 2003) and older children (Rothbart, Ahadi, Hershey, & Fisher, 2001), an analogous instrument appropriate for use with children between the ages of 1 and 3 has not been made available. The current study describes the psychometric characteristics, factor structure, and demographic correlates of an instrument designed to fill this gap: the Early Childhood Behavior Questionnaire (ECBQ).The ECBQ was originally designed to supplement the Toddler Behavior Assessment Questionnaire (TBAQ; Goldsmith, 1996), a widely-used parent-report temperament questionnaire for young children. The TBAQ includes 108 items that address five aspects of temperament: Activity Level, Pleasure, Social Fearfulness, Anger Proneness, and Interest/ Correspondence concerning this article should be addressed to Sam Putnam, Department of Psychology, Bowdoin College, 6900 College Station, Brunswick, ME 04011. Persistence. Goldsmith (1996) documented internal consistency and interrater reliability of the instrument, as well as convergence with other temperament measures. Subsequent studies (e.g., Eiden, Edwards, & Leonard, 2004;Kochanska & Knaack, 2003;Lemery, Goldsmith, Klinnert, & Mrazek, 1999) have provided support for the construct validity of the instrument. The value of this measure is further indicated by successful translations to Japanese (Kusanagi, Chen, & Hoshi, 2000), Spanish (Salinas, Montesinos, & Carnicero, 1999), and Dutch (Van Bakel & Riksen-Walraven, 2004).Several aspects of temperament assessed by the new instrument, but not the TBAQ, reflect differences between our theoretical approach and the approach that guided the creation of the TBAQ. Whereas Gold...