The proportion of older cancer patients is increasing due to demographic and disease-specific reasons. However, this group of patients is severely underrepresented in research and clinical therapy. Limitation in physical and functional capacity with considerable interindividual heterogeneity remains one of the important problems in the treatment decision process. One approach to this problem is the use of a Comprehensive Geriatric Assessment (CGA) to describe and classify these deficits with high validity and reliability. The different domains of CGA are described with special respect to the instruments applied, as CGA has also a key role in the decision process.