Due to demographic changes there is an increasing number of elderly and old patients with cancer. This group of patients shows a significant heterogeneity and differs from the average young patient. Identification of relevant functional deficits and comorbidities remains crucial for an efficient treatment strategy of this patient group. For this reason, the geriatric assessment has been developed and integrated in daily oncological practice. Within this diagnostic approach oncologists can for example identify elderly fit patients suitable for aggressive treatments or identify at-risk patients for complications. Recent studies have shown that this approach is feasible in daily practice and capable of improving outcome. There is still the need for more specific instruments for different cancers.