Bath Ankylosing Spondylitis Disease Activity Index (BASDAI) is a standard instrument regularly used to assess disease activity of patients with ankylosing spondylitis (AS). However, the well-being of a patient is also affected by impairment of function as well as psychological status and other factors. The objective of this study was to evaluate if psychological status, stressful life events, and sleep quality contribute significantly to BASDAI. Six hundred eighty-three AS patients satisfying the Modified New York Criteria for AS were recruited from the rheumatology clinics of seven hospitals in China. Patients with other concomitant disorders were excluded. Participants were requested to complete a set of clinical examinations and the following questionnaires: Bath Ankylosing Spondylitis Disease Activity Index (BASDAI), Bath Ankylosing Spondylitis Functional Index (BASFI), Zung Self-Rating Anxiety Scale (SAS), Zung Self-Rating Depression Scale (SDS), Pittsburgh Sleep Quality Index Questionnaire (PSQI), Health Assessment Questionnaire for Spondyloarthropathies (HAQ-S), and Social Readjustment Rating Scale (SRRS). Spearman correlation analysis showed that BASDAI was highly associated with degree and duration of morning stiffness, overall pain, nocturnal back pain, overall back pain, anxiety, and BASFI (all P < 0.001), but were not associated with education, HAQ-S, and sleep medication in PSQI (P > 0.05). Multiple stepwise regression analysis indicated that overall pain was the maximal statistical contribution in predicting disease activity (standardized coefficient, 0.335). In hierarchic multiple regression analysis, psychological variables added an only additional 2.7 % to the overall R (2) beyond that accounted for by demographic and medical variables, resulting in a final R (2) of 53.5 %. Although BASDAI is a very good measurement of pain and stiffness and to a certain extent effect of functional impairment in AS, it barely takes into account psychological status, stress life events, and sleep quality These factors should be evaluated by other modalities.