BACKGROUND: The Strengths and Difficulties Questionnaire (SDQ) is a valuable screening tool for identifying psychosocial problems. Its performance in a multi-ethnic society, common to many paediatric health care workers, has not been investigated. Because it is important that screening instruments are valid and reliable for all ethnic groups within one society, we examined differences in the SDQ’s psychometric properties in a multi-ethnic society. METHODS: The SDQ parent (n = 8114) and teacher form (n = 9355) were completed as part of a preventive health check for children aged 5-6 years of Dutch and non-Dutch ethnic backgrounds. The Child Behaviour Checklist (CBCL)/Teacher Report Form (TRF) was administered to a subsample. RESULTS: Factor analysis of the parent-rated SDQ showed different rating patterns for two of the five subscales for non-Dutch children as compared with Dutch children. Cronbach’s alpha for the total difficulties score varied by ethnic group (0.73-0.78 parent-rated SDQ, 0.80-0.83 teacher-rated SDQ), and coefficients were generally smaller for non-Dutch than for Dutch children (P < 0.05). Alpha coefficients for subscales varied between 0.31-0.85 for ethnic groups. Inter-rater correlations between parents and teachers for the total difficulties score varied between 0.20-0.41 between ethnic groups and were larger for Dutch than for non-Dutch children (P < 0.05). Concurrent validity was acceptable for most scales and most ethnic groups. CONCLUSION: The total difficulties score of the parent- and teacher-rated SDQ is valid and reliable for different ethnic groups within Dutch society. However, there are differences in reliability and validity of the subscales, which makes interpretation of the subscales difficult for certain ethnic groups.