BACKGROUND: Endemic forms of pemphigus are a unique group of autoimmune diseases that represent opportunities to study interactions of the environment and genetics with the immune system. The restriction to relatively well-defined regions of South and Central America and perhaps Africa characterizes these diseases. OBJECTIVES: The aims of this study were to confirm the endemic nature of a new type of autoimmune disease occurring in a mining town in northeastern Colombia in the El Bagre area, to characterize it, and to compare it with other forms of endemic pemphigus. METHODS: A 10-year prospective, controlled epidemiologic, humanitarian, and immunologic fieldwork case-control survey was performed in El Bagre, Colombia. RESULTS: Our work revealed that this disease is endemic in rural areas surrounding El Bagre. The disease appeared in 4.7% of middle-aged and older men and postmenopausal women from these rural areas. This disease differs from previously described forms of endemic pemphigus. It shares some heterogeneous immunoreactivity with paraneoplastic pemphigus but is not associated with malignant tumors. The disease resembles Senear-Usher syndrome (pemphigus and lupus) but occurs endemically either with a localized stable clinical course or in a systemic form. This systemic form may affect organs other than skin and is characterized by episodic relapses and poor prognosis in comparison with the localized form. CONCLUSION: We have confirmed endemic pemphigus foliaceus in El Bagre as an autoimmune disease that shares features with Senear-Usher syndrome but occurs in an endemic fashion. Heterogeneous antigenic reactivity is observed as in paraneoplastic pemphigus but with no evidence of association with neoplasia. In addition, constant exogenous antigenic stimulation and a genetic predisposition may be required in the pathogenesis of this disease.