Atopic dermatitis is often the first and most prevalent manifestation of atopic disease in preschool children. The objectives of the present study were to determine the prevalence and severity of atopic dermatitis in 2-year-old children. Questionnaire data from a total population of 4784 two-year olds and data from a clinical investigation of a sub-sample of 390 children were obtained from a comprehensive prospective study (Prevention of Atopy among Children in Trondheim). The severity of the atopic dermatitis was scored both according to the Nottingham Eczema Severity Score and the Severity Scoring of Atopic Dermatitis. In the total population the prevalence of this disease, defined as any eczema and itchy rash was 16.5% (95% CI: 15.5-17.6). In the subsample, the corresponding prevalence was 20.6% (95% CI: 16.6-24.6) and 15.9% (95% CI: 12.3-19.5) when diagnosed by the UK Working Party's Criteria. More than 70% of the children with UK-diagnosed atopic dermatitis had mild disease according to both the Nottingham Eczema Severity Score and the Severity Scoring of Atopic Dermatitis. The prevalence of atopic dermatitis among 2-year olds was high. However, more than two-thirds of the children had mild disease, which may imply that the impact of atopic dermatitis as a risk factor for future atopic disease is limited.