OBJECTIVES: To evaluate child development, social competence, like intellectual ability, is an important aspect. The social competence of a child is prescribed by behaviors suitable for the society (adaptive behaviors) and behaviors not suitable for the society (maladaptive behaviors). The Vineland Adaptive Behavior Scales (VABS) have been widely administered to children in a semi-structural interview to evaluate social competence. The Social Competence test (S-M test) widely used in Japan is a translated version of the Vineland Social Maturity Scale for adaptive behaviors. Since only the region of adaptive behaviors was translated into Japanese, we attempted to develop a Maladaptive Behavior Scale in Japanese based on the VABS to evaluate the social competence of children. METHODS: The Maladaptive Behavior Scale of the VABS was translated into Japanese and back-translated to ensure appropriate translation. It was administered to children belonging to the birth cohort of the Tohoku Study of Child Development at the age of 66 months. The subjects for analysis in this study were 451 children (230 boys, 221 girls). RESULTS: To assess internal consistency, we used the standardized Cronbach alpha coefficient and the result was 0.81. The correlation coefficient between the scores of the S-M test and those of the Maladaptive Behavior Scale was -0.15. The correlation coefficient between the scores of the Child Behavior Checklist at 30 months and those of the Maladaptive Behavior Scale was 0.44. CONCLUSION: These results suggest that the Maladaptive Behavior Scale may be a reliable instrument for assessing maladaptive behavior in Japanese children.