The objective of the study is to investigate the prevalence, distribution and predictors of mental health problems in 5-7-year-old Danish children in the general population. This study is a 5-7-year follow-up study of a birth cohort of 6,090 children, the Copenhagen Child Cohort 2000. The extended version of the Strengths and Difficulties Questionnaire (SDQ) was answered by parents and pre-school teachers. Data from Danish national registers included perinatal data, socioeconomic data and data on child mental illness diagnosed at hospital in preschool age. Register data from the first year of life was obtained from 99.7% of the children in the cohort. Of 5,898 eligible children, 3,501 participated in the SDQ assessment (59%). The overall estimated 6-month prevalence of mental health problems was 4.8% (95% CI 4.1-5.6). Conduct problems were found in 3.0% (95% CI 2.4-3.6), problems of hyperactivity/inattention in 0.7% (95% CI 0.4-1.0) and emotional problems in 1.5% (95% CI 1.1-1.9). Boys showed a higher risk of having mental health problems as compared to girls: risk ratio 2.0 (95% CI 1.5-2.8). Several markers of socioeconomic disadvantages were associated with mental health problems at 5-7 years of age. In conclusion, the 6-month prevalence of SDQ-measured mental health problems was relatively low in Danish children when compared with findings from several European countries, but was in line with findings from other studies in Nordic countries. The lower prevalence might reflect differences in psychosocial risk load and environmental stress given the social and cultural context.