The sick building syndrome (SBS) has been the subject of serious scientific inquiry only in the past 10 years. It is commonly accepted to represent eye, nose, and throat irritation; headaches, lethargy, difficulty concentrating, and sometimes dizziness; nausea, chest tightness; and other symptoms. Evidence suggests that what is called the SBS is at least three separate entities, each of which has at least one cause. This review will summarize the epidemiologic investigations of the SBS and present an overview of etiologic hypotheses.