An allergic disposition has long been recognized as a risk factor for asthma. However, it has been suggested that, irrespective of genetic factors, exposure to environmental agents is of major importance in the development of asthma. In industrialized countries, people spend most of their time indoors and so environmental conditions inside the home may play an important role in asthma development. A review of studies examining the relationship between housing conditions and health in general or, more specifically, the relationship between respiratory symptoms/asthma and damp housing and mould has been carried out. These studies have shown that damp housing conditions are associated with increased prevalence of respiratory symptoms and asthma. The severity of asthma increases with an increasing quantity of dampness and mould in the home. It is suggested that damp conditions may, by a number of mechanisms, increase the allergenic burden so resulting in the development of asthma.