There is increasing evidence that indoor exposure to mould is associated with health disorders. Components of mould spores are discussed to induce respiratory diseases, including asthma, allergies, but also symptoms of the Sick-Building-Syndrome (SBS) like irritation of mucous membrane and headache. Within epidemiological studies the impact of mould exposure on health outcome has been investigated. Clinical effects were estimated using clinical examinations and questionnaires, in case of children self-administrated by parents. Lung function was tested. Exposure (close to the patients/study participants) of mould spores and MVOC (microbial volatile organic compounds) were observed. Exposure to Penicillium lead to a higher risk for respiratory diseases and asthma, Aspergillus exposure was associated with a higher risk for allergies. There were a strong correlation between MVOC and SBS symptoms. Additionally it could be shown an impact on lung function by MVOC exposure. Moulds do not act only as allergen. General immunosuppressive properties of some fungal metabolites, such as mycotoxins and MVOC, demonstrated the possibility of non-specific effects on the immune system.