OBJECTIVE: To assess the effectiveness of rehabilitation in a group of patients with active ankylosing spondylitis (AS) by the Assessment in Ankylosing Spondylitis (ASAS) Working Group response criteria. METHODS: Fifty-two active AS patients consecutively admitted to a rehabilitation inpatient clinic were enrolled. Patients underwent a 3-week intensive rehabilitation programme and were then discharged with home exercises. The primary outcome measure was the proportion of patients achieving a response based on ASAS 20 at discharge, and at 6 and 12 weeks after. Secondary outcome measures included an improvement in the Revised Leeds Disability Questionnaire (RLDQ) and function expressed as anthropometric measures. RESULTS: The ASAS 20 was achieved in 46 patients (88.5%) at the end of the rehabilitation, in 31 (59.6%) and in 17 (32.7%) patients at 6 and 12 weeks follow-up, respectively. The percentage of ASAS 20 responders statistically declined over time measured from the end of rehabilitation compared with 6 (P < 0.001) and 12 weeks follow-up (P < 0.001). Conclusion: The present study shows the effectiveness of rehabilitation as assessed by the ASAS 20, a validated instrument for treatment response, suggesting its usage in rehabilitation settings. Moreover, the results obtained show that the effectiveness of the intensive inpatient rehabilitation declined over time.