This study aimed to clarify the characteristics of the Japanese version of the Infant-Toddler Social and Emotional Assessment (J-ITSEA), a parentreport questionnaire concerning social-emotional/behavioral problems and delays in competence in 1- to 3-year-old children. The differences in score between genders, ages, and between the J-ITSEA and the original Infant-Toddler Social and Emotional Assessment were examined. The data of 617 participants recruited from Saitama prefecture through stratified two-stage sampling were analyzed. The Cronbach's alpha ranged from 0.76 to 0.93. Gender differences emerged for some problems and all competence scales, with boys rated higher in the Externalizing problem domain and Activity/Impulsivity subscale and girls rated higher in the Internalizing problem domain, Inhibition to Novelty subscale, and all Competence scales. The Competence domain score increased across age groups. Compared with a normative sample in the US, participants in this study rated higher in Aggression/Defiance and Separation Distress, and rated lower in Peer Aggression and most of the Competence scales. The results indicate that the J-ITSEA scores should be interpreted in comparison with standard scores assigned for gender and 6-month age groups, and that specific criteria for the cut-off points for the J-ITSEA are required instead of those in the original questionnaire.