Abstract: Mannose-Binding Lectin (MBL) is a member of the collectin family. It binds to various oligosaccharides and activates the classical pathway of complement independent from C1q. The aim of present study is to study the distribution of the alleles of MBL gene and promoter variants in intracellular, extracellular pathogens and autoimmune diseases. Our studies showed occurrence of the codon 54 mutation (allele B) of MBL was associated with the occurrence of the acute hepatitis C, this showed the low MBL level can intense progress of this infection, but in other intracellular infections, low expression MBL genotypes associated with protection against these infections and wild type alleles with high MBL production considered as a risk factor for these intracellular pathogens. In extracellular pathogens, there was contrary and wild types of genotype with high production of MBL were associated with protection against these infections and alleles with low MBL production considered as a risk factor for these pathogens. In autoimmune diseases our study and other studies demonstrated that low MBL was a risk factor for these diseases.