PURPOSE: Review of the literature on epidemiologic data of sarcoidosis and risk factors. CURRENT KNOWLEDGE AND KEY POINTS: Epidemiological data show that sarcoidosis is a world-wide disease. Frequency is influenced by multiple predisposition factors. The most important are racial factor, sex, age, familial aggregation, genetic factor and/or infective agent. One of these is insufficiency. FUTURE PROSPECTS AND PROJECTS: Patent sarcoidosis is revealed when concomitant environmental factors (infective agent, climate, country) and predisposition ones (race, sex familial aggregation) appear together and inducing, in each patient, a particular sarcoidosis.