BACKGROUND: Although child mental health problems are among the most important worldwide issues, development of culturally acceptable mental health services to serve the clinical needs of children and their families is especially lacking in regions outside Europe and North America. The Strengths and Difficulties Questionnaire (SDQ), which was developed in the United Kingdom and is now one of the most widely used measurement tools for screening child psychiatric symptoms, has been translated into Japanese, but culturally calibrated norms for Japanese schoolchildren have yet to be established. To this end, we examined the applicability of the Japanese versions of the parent and teacher SDQs by establishing norms and extending validation of its psychometric properties to a large nationwide sample, as well as to a smaller clinical sample. METHODS: The Japanese versions of the SDQ were completed by parents and teachers of schoolchildren aged 7 to 15 years attending mainstream classes in primary or secondary schools in Japan. Data were analyzed to describe the population distribution and gender/age effects by informant, cut-off scores according to banding, factor structure, cross-scale correlations, and internal consistency for 24,519 parent ratings and 7,977 teacher ratings from a large nationwide sample. Inter-rater and test-retest reliabilities and convergent and divergent validities were confirmed for a smaller validation sample (total n = 128) consisting of a clinical sample with any mental disorder and community children without any diagnoses. RESULTS: Means, standard deviations, and banding of normative data for this Japanese child population were obtained. Gender/age effects were significant for both parent and teacher ratings. The original five-factor structure was replicated, and strong cross-scale correlations and internal reliability were shown across all SDQ subscales for this population. Inter-rater agreement was satisfactory, test-retest reliability was excellent, and convergent and divergent validities were satisfactory for the validation sample, with some differences between informants. CONCLUSIONS: This study provides evidence that the Japanese version of the SDQ is a useful instrument for parents and teachers as well as for research purposes. Our findings also emphasize the importance of establishing culturally calibrated norms and boundaries for the instrument’s use.