In a little-noticed outcome of President Barack Obama’s Affordable Care Act, jails and prisons around the country are beginning to sign up inmates for health insurance under the law, taking advantage of the expansion of Medicaid that allows states to extend coverage to single and childless adults — a major part of the prison population.

State and counties are enrolling inmates for two main reasons. Although Medicaid does not cover standard health care for inmates, it can pay for their hospital stays beyond 24 hours — meaning states can transfer millions of dollars of obligations to the federal government.

But the most important benefit of the program, corrections officials say, is that inmates who are enrolled in Medicaid while in jail or prison can have coverage after they get out. People coming out of jail or prison have disproportionately high rates of chronic diseases, especially mental illness and addictive disorders. Few, however, have insurance, and many would qualify for Medicaid under the income test for the program — 138 percent of the poverty line — in the 25 states that have elected to expand their programs.

Health care experts estimate that up to 35 percent of those newly eligible for Medicaid under Obama’s health care law are people with histories of criminal justice system involvement, including jail and prison inmates and those on parole or probation.

"For those newly covered, it will open up treatment doors for them" and potentially save money in the long run by reducing recidivism, said Dr. Fred Osher, director of health systems and services policy for the Council of State Governments Justice Center. He added that a 2009 study in Washington state found that low-income adults who received treatment for addiction had significantly fewer arrests than those who were untreated.

In Chicago, inmates at the Cook County jail are being enrolled in Medicaid under the health care law as part of the intake process after they are arrested; the county has submitted more than 4,000 applications for inmates since Jan. 1. In Colorado, state prisoners are being signed up when they need extended hospitalization; 93 applications for inmates and 149 for parolees have been submitted so far. In the Portland area, more than 1,200 inmates have been enrolled through the state exchange, Cover Oregon, while Delaware and Illinois expect to start soon.