Under the PPACA, all health plans are prohibited from discriminating against or charging higher rates to any individual on the basis of preexisting conditions.
Before the Patient Protection and Affordable Care Act, health insurance companies were allowed to refuse to cover you if you had a preexisting condition, meaning health problems (like asthma, diabetes, or cancer) which are already present and won't simply happen in the future following an accident or disease. In 2010, the PPACA introduced the idea that insurers can no longer turn down anyone, and have to cover children under 19 years old with preexisting conditions without asking them to pay more for coverage.