Rosemary Kennedy, 86, the developmentally disabled oldest sister of President John F. Kennedy, died Jan. 7 at Fort Atkinson Memorial Hospital in Wisconsin.

Miss Kennedy was the oldest of the surviving Kennedy siblings, who include Sen. Edward M. Kennedy (D-Mass.).

Rosemary Kennedy, top, is seen in this 1938 family photo taken in Bronxville, N.Y. (Boston Globe Via AP)

She had lived most of her life in a facility in Wisconsin since undergoing a lobotomy more than 60 years ago.

Miss Kennedy was characterized as slow and shy-seeming from early childhood, possibly dyslexic and apparently retarded. But behavioral problems that began in her early twenties led to the brain operation, according to published accounts.

She was "probably the first mentally retarded person to receive a lobotomy," Jack El-Hai wrote in a 2001 article in The Washington Post Magazine.

A 1987 Post excerpt of a book by historian Doris Kearns Goodwin said that to Miss Kennedy's father, Joseph P. Kennedy Sr., a lobotomy -- a brain operation then regarded as a miracle treatment -- "was an obvious solution" to the frustrations she experienced in trying to find a place for herself in a hard-driving family.

However, according to Goodwin's account, "something went terribly wrong," and she emerged "far worse" than ever.

The institution that was chosen for her, according to the article, was St. Coletta of Wisconsin, near Jefferson. According to a statement St. Coletta issued last night, it aids the developmentally disabled and cared for her for 57 years.

Miss Kennedy liked to send letters to her nephews and nieces, and she visited relatives in Washington and Florida, the statement said. It said she liked visiting the Cape Cod home where she and her sisters and brothers grew up.

In a statement released last night through a spokeswoman for Sen. Kennedy, the family said that Miss Kennedy "has gone today to be with God." Her death was attributed to natural causes.

"She left us peacefully, with her brothers and sisters at her side," it said.

Miss Kennedy was "a lifelong jewel to every member of our family," the statement said, adding that from her earliest years, "her mental retardation was a continuing inspiration to each of us, and a powerful source of our family's commitment to do all we can to help all persons with disabilities live full and productive lives."

Her sister Eunice Shriver is known as the founder of the Special Olympics, and some accounts describe Rosemary as an inspiration for the athletic competition aimed at those with intellectual disabilities.

According to published accounts, Miss Kennedy had been presented to the king and queen of England in the 1930s while her father was the U.S. ambassador.

After the family's return from England, it was reported that her mental skills had deteriorated and her "customary good nature" had given way to violent behavior that no one could understand, Goodwin wrote.

Miss Kennedy was born in Boston in 1918. Her oldest brother, Joseph P. Kennedy Jr., died at 29 on a World War II mission.

President Kennedy was assassinated in 1963 at age 46. Sen. Robert F. Kennedy was 42 when he was assassinated in 1968. Their sister Kathleen, was 28 when she was killed in an airplane crash in 1948.

The surviving sisters are Eunice, 83, Patricia, 80, and Jean, 76. Sen. Kennedy, 72, is the only survivor among the four brothers.