BACKGROUND Atopic dermatitis (AD) is a chronic relapsing disease that has increased in prevalence during the last 4 decades. However, little is known about factors that affect disease severity. METHODS We carried out a longitudinal observational study that included children aged 5 to 10 years recruited from general practices in the United Kingdom. General practitioners identified potential patients and the United Kingdom diagnostic criteria for AD were used to verify the diagnosis in children. The scoring AD index was used to assess disease severity. In addition, information was obtained from parents at the first interview as to age of onset, social class, ethnic group, child's atopy, family history of atopy, and other potential risk factors using a 5-page piloted questionnaire. The aim was to document risk factors for AD severity over time by sequential repeated interview and clinical examination during a 2-year period. The scoring AD index was skewed to the right so nonparametric tests were used for statistical significance. RESULTS In all, 137 children (65 boys [47%] and 72 girls) with AD were recruited and seen up to 4 times; 40 in March 1998, 104 in October 1998, 116 in March 1999, and 120 at the final visit in October 1999, giving our study an 88% follow-up rate. The severity scores were ranked into 3 categories (80% mild, 18% moderate, and 2% severe) according to suggested guidelines. From this population we were able to show that those with eczema that commenced during the first year of life, which was accompanied by asthma, hay fever, or both, and associated with living in an urban area, had more severe disease independent of other potential risk factors. CONCLUSIONS This study has systematically studied AD severity in a community-based design. Researchers and clinicians should be aware of those factors reported in our study as patients exposed to these factors may have a different disease outcome. Further studies on disease severity are needed.