Aims: We report on the frequency and the correlations of behaviour problems among children with Down syndrome in preschool-age. Method: As part of a longitudinal study 48 mothers of children with Down syndrome completed the German version of the ‘Strengths and Difficulties Questionnaire’ (SDQ-D) and the Parenting Stress Inventory (PSI). The mothers were asked to fill out the questionnaires when the children had a mean age of five years. The results were compared to norms from children with typical development. Results: Thirty per cent of the children with Down syndrome were rated as abnormal. Specifically, mean scores indicating problems with children of the same age and hyperactivity were elevated. A regression analysis predicting the total problem score of the SDQ-D revealed maternal educational level, optimistic attitude, and subjective parental stress at the age of one year and the degree of behavioural abnormalities at the age of three years as significant influential factors. Conclusion: Early intervention for Down syndrome children should include supporting parenting competence and coping skills in order to prevent behaviour problems.