Members of Congress do not pay for the individual services they receive at the OAP, nor do they submit claims through their federal employee health insurance policies. Instead, members pay a flat, annual fee of $503 for all the care they receive. The rest of the cost of their care, sources said, is subsidized by taxpayers.
Last year, Congress appropriated more than $3 million to reimburse the Navy for staff salaries at the office. Next year's budget allocates $3.8 million for the office, including more than half a million dollars to upgrade the Office's radiology suite. Sources said additional money to operate the office is included in the Navy's annual budget.
In 2008, 240 members paid the annual fee, though some sources say congressmen who didn't pay the fee were rarely prevented from using OAP services.
The OAP refused to comment in detail for this story, and Rear Adm. Brian Monahan, the Attending Physician to Congress, did not return phone calls requesting an interview. When ABC News chief medical editor Dr. Timothy Johnson visited the office in person in September to speak with Monahan, he was asked to leave.
After Johnson's visit, Kyle Anderson, a spokesman for the House Committee on Administration, which partially oversees the OAP, called ABC News and agreed to answer some general questions via e-mail. He refused to discuss the number of staff members who work at the OAP or the type of facilities the OAP makes available to members of Congress.
Requests by ABC News to tour the facility were also denied due to "security sensitivities."
Anderson said members of Congress are treated by specialists from military hospitals who visit the OAP at no charge. Congressmen are also eligible for free out-patient care at military facilities in the Washington, D.C., area, including Walter Reed Army Medical Center and Bethesda Naval Medical Center.
However, Anderson said, "individual health insurance is required for members to see local health professionals."
Rep. Steve Kagen of Wisconsin -- one of 15 medical doctors in Congress -- is the only member of either the House or Senate who has no health insurance coverage. Kagen, a Democrat and advocate for health care reform, said he turned down the plan he was offered through the Federal Employee Health Benefits Program.
"I said, 'I'll tell you what. I respectfully decline. Until you can make the same offer to everyone that I have the honor of representing, I just don't think it's fair," Kagen said he told the congressional staffer who reviewed the plan with him in 2006.
But while Kagen has touted in campaign advertisements and news interviews that he has no health insurance coverage, he has openly admitted he used OAP services. In January, for example, he paid more than $4,000 out of pocket for outpatient arthroscopic knee surgery. After the procedure, he said, he used the attending physician's office and staff to assist him with physical therapy.
"It's one of the, quote, benefits of being in Congress," Kagen said. "They have physicians and nurses that will see you on the spot, on the beck and call."
Kagen said he believed the office was no different than the on-site medical clinics at major corporations. "It's kind of like being at a very large employer, where you have an on-site nurse or an on-site doctor, an on-site capability to get your immunizations or your blood pressure checked."