An international working group was formed to select core sets to be used as endpoints in clinical trials in ankylosing spondylitis (AS). The results of the first steps of the selection of these core sets are described. The definition of the settings for which the core set will be intended are defined. The methods used to select the core sets were a combination of literature search, nominal group discussions, and plenary discussions. The following settings were defined: disease controlling antirheumatic therapy (DC-ART), symptom modifying antirheumatic drugs (SMARD)/physical therapy, and clinical record keeping. Over 110 variables used as endpoints in AS were found in the literature. The preliminary core set for DC-ART consists of physical function, pain, spinal mobility, patient global assessment, peripheral joints/entheses, x-ray spine. The selected core set for SMARD/physical therapy includes physical function, pain, spinal mobility, spinal stiffness, and patient global assessment. The core set for clinical record keeping includes all measures of the SMARD/physical therapy core set completed by peripheral joints/entheses, and acute phase reactants. Three preliminary core sets for AS have been defined. Further research will be performed to select specific measures for all domains.