You wrote it, you own it.
And the Wisconsin Republican insisted that "major components" of that bill will stay in place.
Ryan's comments on Fox Business News came as conservatives and other critics of the bill, which would repeal and replace key parts of the Affordable Care Act, clamored for changes.
Some conservative allies of Trump have called for the president to drop his support for the proposal because of the political perils of shrinking federal financial aid to help people get health coverage.
"Obviously, the major components are staying intact, because this is something we wrote with President Trump, this is something we wrote with the Senate committee," Ryan said.
"This is the plan we ran on all of last year."
The Congressional Budget Office estimated Monday that the bill, if it becomes law, will result in 24 million more people becoming uninsured by 2026 than would be the case under Obamacare. The CBO also noted that lower-income and older people who buy individual health plans would tend to face sharply higher health-care costs.
However, Ryan also said that as the bill moves through the legislative process, "we're making all kinds of improvements and refinements that we think make this bill better."
The bill, dubbed the American Health Care Act, is pending in the House, where it will be reviewed this week by the Budget Committee.
After being introduced last week, the bill instantly drew fire from more conservative members of Congress who said it did not go far enough in repealing Obamacare because it still offers tax credits to help people buy insurance and because it delays a rollback of the expansion of Medicaid.
But a number of moderate Republicans oppose a rollback of Medicaid and are worried about sharp drops in the number of people with insurance. They also have concerns about the bill defunding the family-planning group Planned Parenthood for one year.
Ryan said on Fox Business News that senators will get a crack at making amendments to the bill after it is passed out of the House.