Sarcoidosis is a systemic disease. Clinical manifestations and prognosis are heterogeneous in sarcoidosis patients from various populations. This suggests that genetic factors and/or environmental factors seem to play important roles in the pathogenesis. Sarcoidosis is characterized as a hyperimmune response to unknown agent(s) at the lesion sites. Regarding pulmonary lesions, macrophage-T lymphocyte alveolitis precedes epithelioid cell granuloma formation. In this review, reports presented in international meetings were introduced to compare population differences; we attempted to review the issues which relate to disease susceptibility in patients with sarcoidosis. In addition, we discussed the possible causative agents, whether T cell receptor expression reflects antigen driven immune responses, and what type of biological active materials may be critical in determining the disease activity and/or prognostic factors, with particular focus on the population differences.