The aim of this study was to determine the intima-media thickness (IMT) in carotid arteries and to assess the relation of these values with plasma homocysteine (pHcy) levels and methylenetetrahydrofolate reductase (MTHFR) C677T gene polymorphism in patients with Ankylosing spondylitis (AS). Serum lipids, vitamin B12, folic acid, pHcy and acute phase protein levels were measured in all cases. MTHFR C677T gene polymorphisms were determined, and IMT of main carotid artery were evaluated ultrasonographically in all subjects. Bath Ankylosing Spondylitis Disease Activity Index, Ankylosing Spondylitis Disease Activity score and Bath Ankylosing Spondylitis Metrology Index were used to assess disease activity and spinal mobility. Fifty AS patients (mean age of 36.6 ± 4.79 years) and 50 control subjects (36.34 ± 4.72 years) were included in the study. Plasma homocysteine levels of AS patients and control group were also similar (14.26 ± 9.96 vs. 11.81 ± 5.53 μmol/L). Hyperhomocysteinemia was present in 11 subjects in patient group (22.0 %), while it was seen in 5 subjects in the control group (10.0 %). The MTHFR C677T genotype distribution was as follows: CC 31 (62 %), CT 14 (28 %), TT 5 (10 %) in AS patients. The mean carotid IMT values were also found to be similar between the groups. The most important factor influencing pHcy level was found as MTHFR 677TT genotype. We indicated no difference of atherosclerosis indices revealed by IMT values and pHcy levels AS patients and control subjects. But an association between MTHFR 677 gene polymorphism and pHcy levels was concluded, which may suggest that MTHFR 677 TT polymorphism may be a potential prognostic factor for cardiovascular disease in patients with AS.