According to the newspaper, an experiment in Oregon found that newly insured people went to the emergency room "a good deal more often" than those without insurance:
The study, published in the journal Science, compared thousands of low-income people in the Portland area who were randomly selected in a 2008 lottery to get Medicaid coverage with people who entered the lottery but remained uninsured. Those who gained coverage made 40 percent more visits to the emergency room than their uninsured counterparts during their first 18 months with insurance.
The findings cast doubt on the hope that expanded insurance coverage will help rein in emergency room costs just as more than two million people are gaining coverage under the Affordable Care Act. And they go against one of the central arguments of the law’s supporters, that extending insurance to large numbers of Americans would reduce emergency room use, and eventually save money.
The study's authors were quoted as saying that when services get less expensive, people use them more.
See New York Times report