Metastatic disease is responsible for the majority of cancer related deaths. Tumour-associated carbonic anhydrase IX (CA IX) is a powerful marker to diagnose various types of metastatic cancers including those of cervical, renal, breast and head & neck origin. The precise prognostic role of CA IX in determining local control versus overall survival is complex, although the majority of reports favour CA IX as a marker for poor prognosis in patients with metastatic cancer. Preclinical studies in cell cultures clearly demonstrate that CA IX stimulates features that enhance metastatic properties of cancer cells for example, reducing cell adhesion, increasing motility and migration, inducing vascularisation and activating proteases, in which CA IX-induced acidification of the microenvironment of the tumour is essential. As most findings are consistent with the idea that CA IX is important in metastatic dissemination, small molecular CA IX inhibitors (including fluorescent-tagged or radiolabelled) and monoclonal antibodies targeting the CA IX isoform have been developed. Studies in tumour xenograft models showed that these CA IX-specific inhibitors and antibodies can be very effective in therapy and imaging of a variety of different metastatic cancers.