IMPORTANCE: Bariatric surgery is associated with decreased risk of obesity-related cancer and cardiovascular disease but is typically reserved for patients younger than 60 years. Whether these associations hold for patients who undergo surgery at older ages is uncertain. OBJECTIVE: To determine whether bariatric surgery is associated with a decreased risk of obesity-related cancer and cardiovascular disease in patients who underwent surgery at age 60 years or older. DESIGN, SETTING, AND PARTICIPANTS: Population-based cohort study of patients from Denmark, Finland, and Sweden who underwent bariatric surgery at age 60 years or older without previous malignant neoplasm or cardiovascular disease between 1989 and 2019. Each patient who underwent surgery was exactly matched to 5 patients with nonoperative treatment for obesity of the same country, sex, and age at the date of surgery. Data were analyzed in December 2023. EXPOSURE: Receiving treatment for obesity, including bariatric surgery and nonoperative treatments. MAIN OUTCOMES AND MEASURES: The main outcome was obesity-related cancer, defined as a composite outcome of breast, endometrial, esophageal, colorectal, and kidney cancer, identified from the national cancer registries. The secondary outcome was cardiovascular disease, defined as a composite outcome of myocardial infarction, ischemic stroke, and cerebral hemorrhage, identified from the patient registries. Multivariable Cox regression provided hazard ratios (HR) with 95% CIs adjusted for diabetes, hypertension, peripheral vascular disease, chronic obstructive pulmonary disease, kidney disease, and frailty. RESULTS: In total, 15 300 patients (median [IQR] age, 63 [61-65] years; 10 152 female patients [66.4%]) were included, of which 2550 (16.7%) had bariatric surgery at age 60 or older and 12 750 (83.3%) had nonoperative treatment. During a median (IQR) of 5.8 (2.8-8.5) person-years of follow-up, 658 (4.3%) developed obesity-related cancer and 1436 (9.4%) developed cardiovascular disease. The risk of obesity-related cancer (HR, 0.81; 95% CI, 0.64-1.03) and cardiovascular disease (HR, 0.86; 95% CI, 0.74-1.01) were similar among who underwent surgery and those who did not. Gastric bypass (1930 patients) was associated with a decreased risk of obesity-related cancer (71 patients [3.7%]; HR, 0.74; 95% CI, 0.56-0.97) and cardiovascular disease (159 patients [8.2%]; HR, 0.82; 95% CI, 0.69-0.99) compared with matched controls (9650 patients; obesity-related cancer: 442 patients [4.6%]; cardiovascular disease: 859 patients [8.9%]). CONCLUSIONS AND RELEVANCE: This cohort study found that bariatric surgery in older patients is not associated with lower rates of obesity-related cancer and cardiovascular events, but there was evidence that gastric bypass may be associated with lower risk of both outcomes.