In this study, bone formation markers [alkaline phosphatase (ALP), bone-specific alkaline phosphatase (BALP) and osteocalcin (BGP)] and bone resorption markers [pyridinium cross-links: pyridinoline (Pyd) and deoxypyridinoline (Dpyd)] were studied in 44 patients with ankylosing spondylitis (AS) and in a control group of 41 subjects. The AS group was classified according to duration of disease, erythrocyte sedimentation rate (ESR) values and gender. Urinary Pyd and Dpyd concentrations of the patients were higher than in the control group, concomitant with the lower T-score values of the patients in both the anteroposterior lumbar spine and femoral neck. Although a correlation between markers of disease activity [ESR and C-reactive protein (CRP)] and bone turnover markers was not observed, urinary excretion of Dpyd and Pyd was enhanced in the ESR >20 mm/h subgroup compared with the ESR < or =20 mm/h subgroup. A significant elevation of urinary Dpyd was also observed in the female subgroup and long disease duration subgroup. Serum ALP, BALP and BGP levels of the patients and control group were not statistically different (p>0.05). No significant differences were observed between mineral and calcitropic hormone levels in either group, and total testosterone levels of the patients were within the reference range. According to this study, urinary Pyd levels are elevated in patients with AS. Gender, duration of disease and ESR also have an impact on urinary excretion of these collagen compounds. It can be concluded that bone turnover in patients with AS reflects normal osteoblastic activity and high osteoclastic activity.