OBJECTIVE: This study aimed to examine the association of eczema, asthma and hay fever with mental health in a general child population and to assess the influence of parental socioeconomic position on these associations. METHODS: We conducted a cross-sectional health survey of children aged 3, 6, 11 and 15 years in the City of Copenhagen, Denmark. Individual questionnaire data on eczema, asthma, and hay fever and mental health problems assessed using the Strengths and Difficulties Questionnaire (SDQ) was linked to register data on demographics and parental socioeconomic position. 9215 (47.9%) children were included in the analyses. RESULTS: Linear regression analyses showed that children with current eczema symptoms had higher SDQ scores (mean difference, 95% CI) of emotional problems (0.26, 0.12 to 0.39), conduct problems (0.19, 0.09 to 0.29) and hyperactivity problems (0.32, 0.16 to 0.48); children with current asthma symptoms had higher SDQ scores of emotional problems (0.45, 0.32 to 0.58), conduct problems (0.28, 0.18 to 0.38) and hyperactivity problems (0.52, 0.35 to 0.69); and children with current hay fever symptoms had higher SDQ scores of emotional problems (0.57, 0.42 to 0.72), conduct problems (0.22, 0.11 to 0.33), hyperactivity problems (0.44, 0.26 to 0.61) and peer problems (0.14, 0.01 to 0.26), compared with children without current symptoms of the relevant disease. For most associations, parental socioeconomic position did not modify the effect. CONCLUSIONS: Children with eczema, asthma or hay fever had more emotional, conduct and hyperactivity problems, but not peer problems, compared with children without these diseases. Atopic diseases added equally to the burden of mental health problems independent of socioeconomic position.