Abstract:[Objective] To explore the cause of delayed diagnosis of spinal fractures in ankylosing spondylitis (AS) . [Methods] The pa- tients with delayed diagnosis(DD) for spinal fracture were searched in our hospital from 2008 to 2019. The fracture characteristics and the causes of DD were analyzed. [Results] From 2008 to 2019, a total of 63 573 patients with spinal diseases were admitted to our department, and among them 3 363 patients (5.29%) were finally diagnosed with spinal fractures. Of the 3 363 patients with spinal fracture, 166 patients (4.94%) were finally diagnosed AS. Among 157 patients who were finally diagnosed of AS spinal fracture, 7 patients were of delayed diagno- sis, accounting for 4.67%, including 3 cases who were misdiagnosed initially in other hospitals, accounting for 1.91%, and 4 cases who were misdiagnosed primarily in our hospital, accounting for 2.25%. The ratio of no definite trauma history in the delayed diagnosis group was sig- nificantly higher than in the confirmed diagnosis group, with a statistically significant difference (P<0.05) . Among the 7 delayed diagnosed patients, 3 patients had one fracture misdiagnosed because of multiple spinal fractures, 2 patients were slightly delayed due to non-obvious symptoms of trauma, 1 case was treated for local malformation due to thoracolumbar fracture during spinal cord injury rehabilitation, 1 case of cervical vertebra facture was misdiagnosed due to incomplete malformation on imaging examination. [Conclusion] Delayed diagnosis of spinal fracture in AS often occurs in patients with multiple spinal fractures, additionally, overlooked occult fracture and delayed presenta- tion are also common reasons for initial misdiagnosis.