Demographic changes have resulted in an increasing number of old people. Together with the age-dependent increase cancer incidence rates, the number of older people with cancer will increase significantly in the coming decades. In geriatric medicine, a structured systematic assessment has been established to recognize an individual patient's deficits and resources in order to be able to tailor an individualized treatment plan. Research in geriatric oncology has demonstrated that transfer of the geriatric assessment from geriatric medicine to oncology helps to identify patients with age-dependent deficits, independent of their chronological age. Such impairments are also predictive for a higher risk of treatment-associated side effects and poorer survival. In addition, geriatric assessment helps to stratify older cancer patients for treatment and avoid under- and over-treatment. Current research strategies address the question of whether interventions based on the results of the geriatric assessment can improve outcomes relevant to the patients. In the past, patient-relevant outcomes, such as maintenance of the ability to care for oneself, were poorly integrated in oncological trials.