More than a fifth of Pennsylvanians under the age of 65 have a diagnosed, preexisting medical condition that might make it difficult or impossible to buy individual health insurance on the private market, the consumer group Families USA said Friday.

It said 2.3 million people under 65 have preexisting conditions such as cancer, lung disease, or diabetes. The numbers likely are low because some people, especially those who are uninsured or underinsured, may have health problems they don't know about, said Ron Pollack, executive director of Families USA.

The group estimated that 44.7 percent of Pennsylvanians age 55 to 64 have preexisting conditions.

In a telephone news conference obviously meant to bolster support for the newly passed health-care-revision legislation, Pollack said the new law "stops abusive practices" that discriminate against the people who most need health coverage.

Starting in 2014, under the health-care legislation, most people will be required to have health insurance.

U.S. Sen. Bob Casey and U.S. Rep. Allyson Y. Schwartz, both Pennsylvania Democrats, participated in the call.

Pollack said he did not know how many of the 2.3 million currently have to buy individual insurance. Generally, those with health problems can be included in large-company health plans without difficulty. But they can run into trouble if they lose their jobs. They face prohibitively high prices, coverage exclusions, or outright rejection when they try to buy insurance on their own.

"It's inexcusable that we allowed this to persist year after year, decade after decade," Casey said.

The revamped-health-care law prohibits discrimination against people with preexisting conditions. Children will be protected, starting Sept. 23. Adults may become part of a high-risk insurance pool in July. Full legal protections go into effect in 2014.

Pollack said Washington-based Families USA released the report because Americans remained confused about the health-care legislation. His group will report each month on some aspect of the law.

Earlier this month, the group said that 57.2 million Americans have preexisting conditions commonly linked to denial of coverage.

Contact staff writer Stacey Burling

at 215-854-4944 or sburling@phillynews.com.