A comprehensive geriatric assessment (CGA) provides clinicians with detailed information on a patient's physiological age and may aid in the treatment decision-making process. Conducting a CGA, however, is time-consuming, requiring extensive data collection and, in some cases, the involvement of multiple healthcare professionals. The CGA is also not specifically targeted towards assessing patients presenting with neoplastic pathologies. These limitations have precluded this tool's inclusion in routine oncologic practice involving seniors. In order to identify CGA domains most predictive of important cancer-specific outcomes, we conducted a systematic review (PROSPERO registration number CRD42012002476) using MEDLINE, CINAHL, EMBASE and CANCERLIT databases. Studies published in English or French between May 1997 and May 2012, in which a CGA was conducted in patients over the age of 65 initiating cancer treatment, were assessed for eligibility, of which 9 studies were selected for this review. As part of the inclusion criteria, all studies must have assessed, at minimum, the following domains: nutritional, cognitive and functional status, polypharmacy, comorbidities and the presence of geriatric syndromes. In predicting mortality, in at least one study or another, all of the aforementioned CGA domains were found to be significant. Most frequently, however, the following domains were reported for predicting mortality: nutritional status (HR=1.84–2.54), the presence of geriatric syndromes such as depression (HR=1.51–1.81), and functional status (HR=1.04–1.33). With regards to chemotherapy-related toxicity, similar findings were obtained where functional status (OR=1.71–2.47) and the presence of geriatric syndromes, such as impaired hearing (OR=1.67, 95% CI 1.04–2.69), had the most significant predictive value. Only one study reported on the incidence of post-operative complications for which severe comorbidity was found to be highly associated with experiencing severe complications (OR=5.62, 95% CI 2.18–14.50), while functional status was found to be significantly associated with experiencing any complication (OR=4.02, 95% CI 1.24–13.09).