In the context of healthcare in the United States, a pre-existing condition is a medical condition that started before a person's health insurance went into effect. Before 2014 some insurance policies would not cover expenses due to pre-existing conditions. These exclusions by the insurance industry were meant to cope with adverse selection by potential customers. Such exclusions have been prohibited since January 1, 2014, by the Patient Protection and Affordable Care Act.
According to the Kaiser Family Foundation, more than a quarter of adults below the age of 65 (approximately 52 million people) had pre-existing conditions in 2016.