The study examined the association between power outages and emergency hospitalizations for cardiovascular (CVD) and respiratory illnesses among 23 million Medicare beneficiaries age 65 and older in the US in 2018. They used the National Outage Dataset to identify days with ≥1% of customers experiencing outages of 8 or more hours. They analyzed county-level daily hospitalization rates using a case-crossover design with a conditional Poisson model that controlled for temperature, precipitation, and wind speed. Power outages have been associated with an increased number of emergency CVD and respiratory hospitalizations. The association with CVD was strongest on the day after exposure (rate ratio RR=1.02, 95% CI: 1.01, 1.03), while with respiratory disease on the day of exposure (RR=1.03, 95% CI: 1.041, 1.041). The data were at the county level, future studies could use a higher spatial resolution. Power outages thus increase the risk of CVD and respiratory hospitalizations in older adults. Improving the reliability of electricity would support community health.