Mitch Dumke / REUTERS
Rep. Jesse Jackson Jr. had been treated at an undisclosed location in Arizona for an undisclosed illness.
Updated at 11:50 p.m. ET: Rep. Jesse Jackson Jr., struggling with an undefined illness in an undisclosed location for nearly a month, has left treatment in Arizona and has entered the world-renowned Mayo Clinic.
In a statement released through the Rochester, Minn. facility, Jackson said he went in for "extensive inpatient evaluation for depression and gastrointestinal issues."
"Congressman Jackson and his family are grateful for the outpouring of support and prayers that have been received throughout his care," reads a portion of the statement.
Further information would be released as his evaluation proceeds, it said.
Jackson in 2004 underwent gastric bypass surgery, though he kept the procedure a secret for several months.
His absence began in late June with an announcement that he was being treated for exhaustion. Since then only the barest of details have been released.
About a week later, Jackson's office issued a statement noting the congressman's condition is "more serious than we thought and initially believed." Another week went by before an email attributed to Jackson's doctor said the congressman is suffering from "mood disorder."
The doctor noted he is responding positively to "intensive medical treatment at a residential treatment facility."
The congressman’s office added that rumors about Jackson Jr. being treated for alcohol or substance abuse "are not true," but a family friend told NBC News that he has severe clinical depression, a drinking problem or a problem with alcohol and was undergoing treatment in Arizona.
Since his absence began, many have called for more information about Jackson's whereabouts and ailment.
“I think Congressman Jackson and his office and his family would be well advised to advise his constituents of his condition," said Democratic Congressman Steny Hoyer a day before news of Jackson's mood disorder surfaced. "He’s obviously facing a health problem."
"[Jackson’s] health is a number one priority,” Sen. Dick Durbin said. "As a public official though, there reaches a point where you have a public responsibility to tell people what you’re facing and how things are going.”
Gov. Pat Quinn, however, has said he would not call for more information to be released.
"The people of Illinois have good hearts," Quinn said July 11. "I pray for Jesse Jackson Jr. every day."
Jackson's family remains mum on the congressman's exact ailment. His father, Rev. Jesse Jackson, said he is "hopeful" for recovery.
"As a father, I offer no medical diagnosis, only the unconditional love of his family," he said.