This study describes the striking similarities seen across three studies examining health service use and associated costs among community-living older adults with comorbidity and one of dementia, diabetes, or stroke, using linked administrative databases from Ontario, Canada. We identified 376,434 persons with diabetes, 95,399 with dementia, and 29,671 with stroke (2008). Comorbidity prevalence differed, with 75% of the stroke cohort having 3+ comorbidities, compared to 50% for dementia and 46% for diabetes. However, in all three, hypertension and arthritis were most common with a frequency over 75%. Overall utilization increased with comorbidity for the three index conditions. Although per-patient costs differed (highest for stroke, then dementia and diabetes), the relative pattern of costs over time was similar. In each cohort, total service costs increased with comorbidity, with acute care services increasing the most. Although intensity of comorbidity differed among the cohorts, we found similar relationships between comorbidity, utilization and costs.