The documents show the agency was gathering details from informants on how Lana Peters' arrival was affecting international relations at that time. She was known as Svetlana Alliluyeva before her defection.
The files were released Monday to The Associated Press under a Freedom of Information Act request.
Peters died last year, aged 85, in a Wisconsin nursing home.
The FBI's file mainly contains memos and news articles from the late 1960s. One 1967 memo details a conversation with a confidential source who said Peters' defection would have a "profound effect" on anyone else considering such a move from the Soviet bloc.
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