At the Indian Health Service hospital in Pine Ridge, S.D., a 57-year-old man was sent home with a bronchitis diagnosis—only to die five hours later of heart failure. When a patient at the federal agency’s Winnebago, Neb., facility stopped breathing, nurses responding to the “code blue” found the emergency supply cart was empty, and the man died. In Sisseton, S.D., a high school prom queen was coughing up blood. An IHS doctor gave her cough syrup and antianxiety medication; within days she died of a blood clot in her lung.

In some of the nation’s poorest places, the government health service charged with treating Native Americans failed to meet minimum U.S. standards for medical facilities, turned away gravely ill patients and caused unnecessary deaths, according to federal regulators, agency documents and interviews.

The IHS, a unit of the Department of Health and Human Services, operates a network of hospitals and clinics, much like the Veterans Health Administration. Under U.S. treaties that date back generations, the service is legally responsible for providing medical care to about 2.2 million tribal members.

But that system has collapsed in the often-remote corners of Indian Country, where patients live hours from other medical providers, often have no insurance and depend on the federal service.

“We’ve lost faith in the IHS, but we have no alternatives to go anywhere else,” said Lisa White Pipe, a tribal council member for the Rosebud Sioux, whose father died last year after a delay in cancer treatment that she blames on the agency. Read more about his and other cases, and see the regulator’s reports.