Background: Previous studies have investigated the natural course of cow’s milk protein allergy (CMPA) and development of atopic diseases into adolescence. Studies with long term follow-up into adulthood are lacking. The aim of this study was to investigate 1) the natural course of CMPA in a 1-year birth cohort of Danish children from birth until 15 and 26 years of age and 2) the development of atopic diseases in a group of children with CMPA (group A) compared to a random sample of 276 children from the same birth cohort (group B). 
Methods: A birth cohort of 1,749 newborns, was investigated prospectively for the development of CMPA and atopic diseases. During the first year of life and at 18 months and 3, 5, 10, 15, and 26 years of age, questionnaire based interviews, physical examination, skin prick tests and specific IgE testing, and from 10 years also spirometry, were carried out. 
Results: 39 (2,2%) were diagnosed with CMPA. The recovery rate was 87%, 92% and 97% at 3, 5 and 26 years of age. Compared to group B, group A had significantly (p < 0,05) higher prevalence of asthma and rhinoconjunctivitis at 15 years of age and at 26 years of age, group A had significantly higher prevalence of asthma and atopic dermatitis. The follow-up rate was 85% (A) and 70% (B). 
Conclusion: CMPA has a good prognosis regarding recovery rate. CMPA and sensitization in early childhood predict sensitization and persistence of allergic diseases into adulthood.