According to a recent report, 18% of U.S. adults visited ...

... an emergency room at least once in 2014, giving the following reasons for their most recent ER visit:

• 77% - seriousness of the medical problem
• 12% - their doctor's office was not open
• 7% - lack of access to other providers
• 4% - no reason given

Source: "Reasons for Emergency Room Use Among U.S. Adults Aged 18–64: National Health Interview Survey, 2013 and 2014," National Health statistics Reports Number 90, Centers for Disease Control and Prevention, February 18, 2016, http://www.cdc.gov/nchs/data/nhsr/nhsr090.pdf