This document is a revision of the guideline on clinical investigation of medicinal products for the treatment of ankylosing spondylitis (CPMP/EWP/4891/03) which came into effect in May 2009. It should be considered as general guidance on the development of medicinal products for the treatment of axial spondyloarthritis and should be read in conjunction with other European and ICH guidelines which may apply to this disease area and patient population.