With a bachelor's degree in French and African studies from Seattle University, Philip Pantaleo, 24, headed to France in 2010 to teach English.

But his health began to deteriorate, and he was tested for digestive disorders through the free universal health-care system. When he returned home, and received more care, he was bombarded with bills.

Given his medical problems, Pantaleo said he would be under a "mountain of debt" if he didn't have health insurance under his father's plan.

"It would be two- to three-thousand dollars covering bills. Given the fact I'm on a stipend of a thousand dollars a month, I can't afford those medical costs," said Pantaleo, of South Park, who now works with a forest-conservancy group.

Pantaleo and millions of other young adults covered under their parents' health insurance are nervously awaiting the U.S. Supreme Court's decision on the constitutionality of the federal Affordable Care Act. If the court throws out the law, many will lose coverage.

Some people, such as those who would be covered by the act's pending expansion of Medicaid, are yet to personally experience the law's benefits. But other provisions — such as those allowing young adults to be covered under their parents' plans until age 26 — are in effect.

Since the law's passage, the number of people ages 19 through 25 with health insurance has soared from 64 percent in 2010 to 75 percent, according to the U.S. Department of Health and Human Services.

Under the federal law, young adults up to age 26 can remain on their parents' plan even if they are out of school, married or living on their own if they cannot get health insurance through an employer. Before the law, many plans removed children by age 19 unless they were full-time students.

After the federal law went into effect two years ago, some states, including Washington, passed similar legislation. The law in Washington resembles the federal law, but covers only state-regulated health plans.

Only the federal law applies to young adults covered under their parents' self-insured, out-of-state and national plans, so if the law is overturned or the provision removed, some in Washington will lose coverage — unless their respective plans decide to keep them.

Many Seattleites work for large corporations, which often opt for national plans to cover employees wherever they work in the U.S. Pantaleo's father has a national plan, so his son is covered until age 26 under federal law, but not state law.

Like Pantaleo, Katie Malmberg, 21, of Wenatchee, is on her father's national health plan. A 2011 George Washington University graduate, Malmberg juggles a part-time job at Macy's and an internship at a museum.

"Even though I'm healthy now, a lot of reasons health insurance is important is because of the preventative stuff," she said. "Girls my age need gynecologists."

And, she said, there has been skin cancer in her family, and she's conscious of the need for early detection.

"It's important that people up until mid-20s have health insurance," Malmberg said. "You need that extra help. It wasn't always this hard. It's really hard to get started now. I definitely have a lot of co-workers who are 25 and are grateful for it."

Her father, Greg Malmberg, 58, a retired maritime engineer, said his wife and 25-year-old son are also on his plan. His son recently nabbed a teaching assistant's job, which the family hopes will lead to his own insurance coverage.

For now, though, Malmberg worries a court decision could leave his children uninsured.

"My kids will be off insurance, and if they got a serious illness or into an accident, it will break the bank," he said. "Hopefully that won't happen, and hopefully they will find insurance."

Kibkabe Araya: 206-464-2266 or karaya@seattletimes.com.