This study aims to investigate how well the Assessment of SpondyloArthritis international Society (ASAS)/Outcome Measures in Rheumatology Clinical Trials (OMERACT) core set and response criteria for ankylosing spondylitis (AS) have been implemented in randomized controlled trials (RCTs) testing pharmacological and non-pharmacological interventions. A systematic literature search was performed up to June 2013 looking for RCTs in patients with axial spondyloarthritis (SpA) (AS and non-radiographic axial SpA). The assessed domains and instruments belonging to the core sets for disease-controlling anti-rheumatic therapy (DC-ART) and symptom-modifying anti-rheumatic drugs (SMARDs) were extracted. Results were reported separately for those trials published until 2 years after the publication of the core set (1 April 2001; 'control trials') and those trials published at least 2 years after the publication date ('implementation trials'). One hundred twenty-three articles from 99 RCTs were included in the analysis, comparing 48 'control trials' and 51 'implementation trials'. Regarding DC-ART core set, the following domains were significantly more frequently assessed in the 'implementation group' in comparison to the 'control group': 'physical function' (100 vs 41.7 %; p ≤ 0.001), 'peripheral joints/entheses' (100 vs 33.3 %; p ≤ 0.001) and 'fatigue' (100 vs 0 %; p ≤ 0.001). Three instruments were significantly more used in the 'implementation group': Bath Ankylosing Spondylitis Functional Index (BASFI) (100 vs 8.3 %; p = ≤ 0.001), CRP (92.3 vs 58.3 %; p = 0.01) and Bath Ankylosing Spondylitis Metrology Index (BASMI) (53.8 vs 0 %; p = 0.001). Regarding SMARD core set domains, physical function (92 vs 23 %; p ≤ 0.001) and fatigue (84 vs 17 %; p ≤ 0.001), as well as the instruments BASFI (88 vs 14 %; p ≤ 0.001) and BASMI (52 vs 0 %; p ≤ 0.001), increased significantly in the 'implementation group'. Twenty per cent of trials from the 'implementation group' but none from the 'control group' included all domains of the core set. In conclusion, this study provides evidence for the implementation of the ASAS/OMERACT core set in RCTs of both DC-ART and SMARD. This applies to the use of the domains and, to a lesser extent, to the specific instruments.