How to account for the appeal of these diaries? I first read them 15 years or more ago, when the world they described  New York from 1976 to 1987  was already dead. I feared that the further passage of time would have done them no favours, and that the antics of a bewildering number of groupies, socialites and spoiled brats whose time has passed would now leave me cold.

On the contrary. "Cabbed to the office ($3). Susan Blond sent a limo for Truman and me to go to the Palladium . . . Truman fixed up a Jack Daniel's with milk and this rock and roll manager-type came in the room and started screaming 'Clear the room. Clear the room, we have to talk money.' So everyone left but us, we didn't know where to go, and he said to Truman, 'Didn't you hear me say to clear the room?' And so I said, 'But he's Truman Capote,' and Truman said, 'But he's Andy Warhol,' and the manager said, 'Oh, sorry.'" End of entry.

There's the appeal: he's Andy Warhol. His legacy endures; he invented, for good or ill, a certain part or style of the modern world. (I spoke to a young art student at the Slade the other day and she put it very well: "He seemed to know everything before it happened.") And, more often than most people, Truman Capote is there too. Other people with similarly numerous namechecks: Diana Vreeland, Bianca Jagger, Liza Minnelli, Catherine Guinness . . . This is the kind of book that had two launch parties: one for the text, the other for the (unauthorised) publication of the index, which almost tells you everything you need to know about what kind of book it is.

One does not exactly wish it longer, although it could have been: its 1,000-odd pages represents about a 20th of what, unedited, it could have reached, but there's something about it that makes you strongly suspect that editor Pat Hackett has done a very thorough and sympathetic job.

There is the almost spooky evenness of tone, the flat, affectless voice that is the mirror of Warhol's art. Some might say that his best work was behind him by the time the Diaries start  or that he had never been the same after being shot by Valerie Solanas. They'd have a point, but then you could counterargue that the Diaries are his last great work of art, and no less valuable for having been created with even less visible conscious intent than anything else he produced.

There is much to surprise, though, and I don't just mean Anna Wintour's tears at having an idea rejected for Interview magazine. The first is that Warhol was a more amusing person, and a more human one, than the mask and blond fright-wig might have let on. The deadpan are by no means immune to human feeling, after all. As Hackett notes, he gets nicer as he gets older. Take the time Lou Reed invites him over to his place in 1978. "When we were going in the kids were whispering, 'There's Lou Reed.' He tells them, 'Go kill yourself.' Isn't that great?" (A few lines later one is nonplussed to read Warhol describe Reed as "so sweet and so funny at the same time, so together".)

By the end he is more nervous about his health, believing in crystals and the quacks peddling them (justified, in his own terms, by the power of positive thinking. Not that it did him much good in the end, and indeed he was almost baffled that his crystal didn't prevent someone from snatching his wig from his head at a book signing in 1985, a trauma he endured stoically in public, but which nearly finished him off internally, if we are to believe his account, and I think we should).

And, inescapably, this is the definitive account of New York in its last great heyday, when it was still indisputably the greatest city on earth. I would hope that people read this the way they read Pepys, and for as long afterwards. The parties may have gone silent, the starry cast departed, but these are the bulletins from one who was at all of them  who knew everyone there. And this was from a time before every Joe Schmoe started being famous for 15 minutes.