Objective The aim of this study was to assess whether homozygosity for the 5, 10-methylenetetrahydrofolate reductase (MTHFR) C677T mutation and plasma homocysteine concentration are related to deep vein thrombosis in Behçet's disease (BD) patients. Methods Forty BD patients (23 males, 17 females; mean age 40.2±8.4 years) and 60 healthy controls (HC) (34 males, 26 females; mean age 41.6±6.9 years) were included in the study. Fourteen of the BD patients had a history of deep venous thrombosis (DVT), as confirmed by Doppler ultrasound. Results The rates of homozygosity for the MTHFR C677T mutation in the BD and HC groups were 7.5% and 10%, respectively. The distribution of MTHFR genotypes was similar in the two groups ( p>0.05), and analysis showed that homozygosity for the mutation was not a risk factor for DVT. The mean plasma homocysteine levels were 13.4±4.2 µmol/l for the overall BD patients and 12.6±3.8 µmol/l for HC ( p>0.05). However, the mean plasma homocysteine level in the BD patients with DVT history (15.9±4.6 µmol/l) was significantly higher than the level in the BD patients with no DVT history (12.1±3.3 µmol/l) ( p=0.013) and the level in the HC group (12.6±3.8 µmol/l) ( p=0.025). Conclusion The study results suggest that elevated plasma homocysteine level may play a role in the pathogenesis of venous thrombosis in BD.