Conflicting data have been published about osteoporosis and bone turnover markers in patients with ankylosing spondylitis (AS). The aim of this study was to determine bone mineral density (BMD) of the lateral lumbar spine in a group of male patients with AS and to investigate the relationship between clinical parameters and markers of bone turnover.Thirty-two consecutive AS patients with a mean disease duration of 14.8 years and 32 control subjects were included. Demographic and clinical characteristics were recorded. The Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) was used to determine the activity of disease. BMD was determined for the lateral lumbar spine in both patients and control groups. Serum osteocalcin and urinary N-telopeptide were measured as bone turnover markers in patient and control groups.Although the mean values of lumbar BMD in AS patients tended to be lower than in the control group, the difference was not statistically significant. Osteoporosis was observed in 11 (34.3%) of AS patients and in 2 (6.2%) of the control group. Osteocalcin levels were significantly higher in AS patients in comparison with control subjects (p< 0.05). In the subgroup analysis according to the activity of the disease, erythrocyte sedimentation rate and N-telopeptide levels were significantly higher in the severely active group when compared with that in mild or moderate disease groups. Active AS patients compared with the control group had significantly lower BMD and significantly higher N-Telopeptide levels (p< 0.05). The levels of BASDAI scores and N-telopeptide values correlated significantly with each other.The incidence of osteoporosis is high in AS patients, and patients with active disease are especially at risk for developing osteoporosis. The monitoring of bone turnover markers and disease activity indices may help to predict patients at risk. Prophylactic and therapeutic strategies are needed to struggle against bone loss in patients with this disabling condition.