Innate immunity consists of macrophages, neutrophils, natural killer cells, mucosal immunuglobulins and the comlement system. Mannose binding lectin (MBL) takes part in innate immunity through opsonisation and complement activation. MBL deficiency is associated with some infections and autoimmune disorders. However some studies indicate that MBL deficiency alone is not essential for immunity but it may intensify the clinic picture of an immune deficiency that already exists. This article refers to clincal studies related to MBL and brings up the clinical importance of MBL deficiency. [Archives Medical Review Journal 2013; 22(4.000): 565-574