To compare the effects of care based on comprehensive geriatric assessment (CGA) as a complement to usual care in an outpatient setting with those of usual care alone. The assessment was performed 36 months after study inclusion. Randomized, controlled, assessor-blinded, single-center trial. A geriatric ambulatory unit in a municipality in the southeast of Sweden. Community-dwelling individuals aged ≥ 75 years who had received inpatient hospital care 3 or more times in the past 12 months and had 3 or more concomitant medical diagnoses were eligible for study inclusion. Participants were randomized to the intervention group (IG) or control group (CG). Participants in the IG received CGA-based care for 24 to 31 months at the geriatric ambulatory unit in addition to usual care. Mortality, transfer to nursing home, days in hospital, and total costs of health and social care after 36 months. Mean age (SD) of participants was 82.5 (4.9) years. Participants in the IG (n = 208) lived 69 days longer than did those in the CG (n = 174); 27.9% (n = 58) of participants in the IG and 38.5% (n = 67) in the CG died (hazard ratio 1.49, 95% confidence interval 1.05-2.12, P = .026). The mean number of inpatient days was lower in the IG (15.1 SD 18.4) than in the CG (21.0 SD 25.0, P = .01). Mean overall costs during the 36-month period did not differ between the IG and CG (USD 71,905 SD 85,560 and USD 65,626 SD 66,338, P = .43). CGA-based care resulted in longer survival and fewer days in hospital, without significantly higher cost, at 3 years after baseline. These findings add to the evidence of CGA's superiority over usual care in outpatient settings. As CGA-based care leads to important positive outcomes, this method should be used more extensively in the treatment of older people to meet their needs.