In this study, we evaluated fatigue by using the multidimensional assessment of fatigue (MAF) index in 68 ankylosing spondylitis (AS) patients. To determine the disease activity, functional status and quality of life, bath ankylosing spondylitis disease activity index (BASDAI), bath ankylosing spondylitis functional index (BASFI) and Short Form 36 (SF36) were used respectively. Mander enthesis index (MEI) was used for evaluation of enthesitis. The mean age of the patients was 37.7 (11.1) years. The prevalence of fatigue was 76.5%. There were significant correlations between MAF and BASDAI (P < 0.001), BASFI (P < 0.001), MEI (P = 0.048), pain (P = 0.001), hemoglobin (P = 0.001), ESR (P = 0.035), dorsal Schober's (P = 0.009), occiput-wall distance (P = 0.048). Also MAF was correlated with all dimensions of SF36 except for social function and emotional role. BASFI was found to be the most significant correlated (P = 0.002) parameter with MAF. This study suggests that fatigue is an important symptom in AS and it seemed to occur in severe AS patients. It should appropriately be measured with respect to its intensity with appropriate measures, such as MAF. Moreover, fatigue may increase functional disability, which is already present as a feature of the disease.