Background/objectives: Obesity is associated with increased health care use (HCU), but it is unclear whether this is consistent across all measures of adiposity. The objectives were to compare obesity defined by body mass index (BMI), waist circumference (WC), waist-to-hip ratio (WHR), and percent body fat (%BF), and to estimate their associations with HCU. Subjects/methods: Baseline data from 30,092 participants aged 45–85 years from the Canadian Longitudinal Study on Aging were included. Measures of adiposity were recorded by trained staff and obesity was defined as BMI ≥ 30.0 kg/m2 for all participants and WC ≥ 88 cm and ≥102 cm, WHR ≥ 0.85 and ≥0.90, and %BF > 35% and >25% (measured using dual energy x-ray absorptiometry) for females and males, respectively. Self-reported HCU in the past 12 months was collected for any contact with a general practitioner, specialist, emergency department, and hospitalization. Pearson correlation coefficients (r) compared each measure to %BF-defined obesity, the reference standard. Relative risks (RR) and risk differences (RD) adjusted for age, sex, education, income, urban/rural, marital status, smoking status, and alcohol use were calculated, and results were age- and sex-stratified. Results: Obesity prevalence varied by measure: BMI (29%), WC (42%), WHR (62%), and %BF (73%). BMI and WC were highly correlated with %BF (r ≥ 0.70), while WHR demonstrated a weaker relationship with %BF, with differences by sex (r = 0.29 and r = 0.46 in females and males, respectively). There were significantly increased RR and RD for all measures and health care services, for example, WC-defined obesity was associated with an increased risk of hospitalization (RR: 1.40, 95% CI: 1.28–1.54 and RD per 100: 2.6, 95% CI:1.9–3.3). Age-stratified results revealed that older adult groups with obesity demonstrated weak or no associations with HCU. Conclusions: All measures of adiposity were positively associated with increased HCU although obesity may not be a strong predictor of HCU in older adults.