Several birth cohort studies have been initiated during the past two decades to study environmental and genetic risk factors for atopic dermatitis, asthma and allergic rhinitis. This article summarizes results from the German Multicentre Allergy Study (MAS), which has followed children (initially 1,314) from birth (in 1990) to the present time. The effects of immunizations, allergen exposure, early sensitization patterns as well as upper airway infections on the subsequent development of asthma and atopy at school age are described. Furthermore, candidate gene studies of atopic dermatitis and increased total serum IgE levels on chromosomes 5q, 12q and 17q in MAS-children and their parents are outlined.