Background and aim Overweight is associated psychological problems. Our aim was to examine if overweight is associated with mental health problems even before entering primary school.

Methods Parents of all children born in Oppland County, Norway, in 2001 were invited to complete questionnaires addressing health issues at 5–6 years of age. Height and weight were obtained from the local public health care clinics. Mental health was assessed using the ‘Strengths and Difficulties Questionnaire’ (SDQ) completed by the parents. Overweight and obesity (OWOB) was defined according to the International Obesity Task Force, and children with OWOB were compared with the rest of the cohort.

Results Of 1119 children (62% of invited), 153 (14%) had OWOB. Their mean (SD) body mass index was 18.9 ± 1.72 vs 15.4 ± 1.06, p < 0.0005. Sex distribution was similar (59 vs 51% girls, p = 0.09), but fewer of those with OWOB had mothers with education at college or university level (38% vs 58%, p < 0.0005). On the SDQ, the OWOB group had higher scores on Total Difficulties (5.64 ± 4.38 vs 4.91 ± 3.71, p = 0.032) and Hyperactivity (2.54 ± 1.85 vs 2.18 vs 0.63, p = 0,029), but the differences did not remain significant after controlling for differences in maternal education and sex (Total Difficulties: p = 0.26, Hyperactivity: p = 0.09).

Conclusion Before school entry, overweight was associated with indices of psychological problems, but the effect of overweight was not significant when controlling for sex and mothers’ education.