Behçet's disease (BD) is an autoimmune disease with an unknown etiology and mannose-binding lectin (MBL) is a pattern recognition receptor in the innate immune system, which is associated with some autoimmune diseases. We investigated MBL2 gene polymorphisms and serum MBL levels in BD patients and controls.MBL2 gene polymorphisms in exon 1 (MBL2 54 Gly/Asp, (A/B)), promoter (MBL2 H/L (G-550C), MBL2 Y/X (G-221C)), and 5' UTR region (MBL2 P/Q (C+4T)) were investigated using polymerase chain reaction and restriction fragment length polymorphism in 119 BD patients and 252 healthy controls. Serum MBL levels were measured by enzyme linked immunosorbent assay in 49 BD patients and 102 sex-/genotype-matched controls.No significant difference was found between BD patients and controls in terms of MBL2 polymorphisms and MBL serum levels. However, the presence of genital ulcer and neurologic involvement were found to be associated with MBL2 54 allele A (OR=2.415, OR=6.632, respectively). Eye involvement was found to be related to the presence of the MBL2 54 AA or AB genotypes (OR=12.46), MBL2-G-550C allele H (OR=1.829). High serum MBL level (> or =500 ng/ml) was associated with skin lesions (p=0.002).The frequencies of the four MBL2 genetic polymorphisms examined were not different in BD patients and healthy controls. However, the presence of genital ulcer, eye involvement, and neuro-Behcet's disease were found to be associated with MBL2 polymorphisms that are associated with the production of high levels of MBL or functional MBL.