Purpose: Comprehensive Geriatric Assessment (CGA) can identify health problems in older persons. In addition, CGA includes intervention towards the identified problems. With follow up, more problems may be identified and the interventions can be adjusted. We wanted to compare CGA with or without tailored follow-up in a randomised design. Patients and Methods: Patients 70+ years referred for oncology treatment with four primary tumour sites. Participants were randomised 1:1 to either control group with no follow-up or intervention group with a tailored follow-up by a multidisciplinary team. Primary outcome was adherence to cancer treatment. Secondary outcomes were daily life activities, physical performance and hospitalisation. Results: In total, 363 participants were randomised. After randomisation only 301 were planned to receive specific cancer treatment. Median age was 75 years. Among the 301 participants, 52% of control group vs. 61% of intervention group completed treatment. Risk Rate (RR): 1.16 (95% Confidence Interval (CI): 0.95–1.42), p = .14. The impact varied between the included tumour-sites, p < .01. We found no difference in 90 days physical performance or daily life activities between groups. During the study period, 55% of controls vs. 47% in the intervention group were admitted to hospital, RR: 0.86 (95%CI: 0.69–1.07), p = .19. Conclusion: In frail and vulnerable patients with cancer, a tailored follow-up on CGA showed no differences in ability to complete initially planned cancer treatment. The impact varied between the included tumour sites. We did not find any impact of tailored follow-up on daily life activities, physical performance or hospitalisation.