In the study presented here, we estimated the relationship between ICU admission and outcomes for hospitalized older patients with exacerbation of chronic obstructive pulmonary disease (COPD), exacerbation of heart failure (HF), or acute myocardial infarction (AMI). We performed a retrospective cohort study of all acute care hospitalizations from 2010 to 2012 for U.S. fee-for-service Medicare beneficiaries aged 65 and older admitted with COPD exacerbation, HF exacerbation, or AMI. The primary outcome was 30-day mortality. Secondary outcomes included hospital costs. We found that, among the 1,555,798 Medicare beneficiaries with COPD exacerbation, HF exacerbation, or AMI, 486,272 (31%) were admitted to an ICU. ICU admission was associated with significantly greater hospital costs for HF and AMI, but not for COPD. We concluded that ICU admission did not confer a survival benefit for patients with uncertain ICU needs hospitalized with COPD exacerbation, HF exacerbation, or AMI. These findings suggest that the ICU may be overused for some patients with these conditions. Identifying patients most likely to benefit from ICU admission may improve healthcare efficiency while reducing costs.