The women - Italian sisters who grabbed the book during a trip to London in 1980 - showed up Monday at a hotel in Rome where McCartney was staying, said Geoff Baker, a spokesman for the musician.
They gave the book to an assistant, then waited an hour before the musician came out to meet with them, the Corriere della Sera newspaper reported.
"We have always loved the Beatles," one of the sisters, Paola De Fazi, told the newspaper. "Seeing Paul ... and talking to him was a dream."
The women, now in their 30s, had attended his concert outside the Colosseum on Sunday.
The diary contains drawings and personal notes, along with references to meetings with the press, anniversaries and appointments with other members of the Beatles, according to Corriere della Sera and another newspaper, La Repubblica.
On March 12, 1970, McCartney drew two hearts and wrote "Happy Anniversary," to his late wife Linda. In another entry, dated April 10 of that year, he wrote: "Paul leaves Beatles."
The sisters said they hadn't planned to steal from him when they went to see his house. "There was some restructuring work going on, and the gate was open," the other sister, Francesca De Fazi, said. "We mustered up our courage and went inside."
Besides the diary, the sisters took a pair of boots and sheet music, then fled. It is not known what happened to the other items they stole.
McCartney played a benefit concert inside Rome's Colosseum on Saturday, followed the next day by a free performance for an estimated 200,000 fans outside the ancient arena.