There was a short story I read in an anthology, damned if I can remember the title or the author or even the title of the anthology, in which a researcher discovers the cure for cancer which has the side effect of changing one’s sex. IIRC it’s a pretty quick outpatient procedure. The guy is disgusted and spends the rest of his career trying to eleminate the sex change from his cure. In the meantime, it’s embraced by the whole world and eventually most everyone in the world starts swapping sexes back and forth just because. In the end the guy gets colon cancer but still refuses to take his own cure, and in his dying moments realizes he’s wrong about sex change being a bad thing but it’s too late and he dies bleeding from the ass.
To be fair, so is everyone else. It’s that kind of place.
There’s a hint of it in David Gerrold’s “The Man Who Folded Himself,” where the guy does so much alternate-history time-travel, he finds realms of “what if” where he, while still “himself,” is of the other sex.
And, of course, there’s Isaac Asimov…
“Clone, clone of my own,
with the Y-Chromosome changed to X.
And when we’re alone,
me and my clone,
we will think about nothing but sex.”
Storm Constantine’s Wraeththu series is about the eponymous hermaphroditic superior quasi-vampiric species that comes to replace/dominate humanity, whose members are all initially human males changed into hermaphrodites (they can also reproduce hermaphroditically with each other, it is later discovered)
Changes, in the collection Smoke and Mirrors, by Neil Gaiman
If clones count, some of the people having themselves cloned in the Vor series get all kinds of body changes, including having the clone be a different sex than the original. This includes both the people who expect to have their brain transplanted to the new body and those who use cloning as a means of reproduction.
Sidebar: Is it “Nine Worlds”? I’ve always heard it referred to as “Eight Worlds”.
I do love me some Varley.
Wow, that sounds like an easy one. If you’re, say, a man with cancer who wants to remain a man, then you just take the cure twice, to change into a woman and then change back. Sure, you’d have a recovery period where your body isn’t the way you would like it, but that’s hardly new for medical procedures.
The guy in question was vehemently opposed to changing even temporarily - IIRC, it was a religious objection. By the time he dies, human had already altered to be androgynous transhumans - he perceives them as angels as he’s dying.
I read a Whitley Streiber book ages ago, Majestic probably? At the end a ufo abductee is gender changed man->woman while moving on to higher things. Probably got the details wrong it was a long time ago!
You’re right, of course. It should be “Eight Worlds.” I love Varley too - wish he’d get back to the promised sequel to Steel Beach and Golden Globe (supposed to be called Irontown Blues, I think).
The Encyclopedia of Science Fiction has an article on the subject:
Not just clones in that universe, regular sex changes, too. In one book, noblewoman Lady Donna Vorrutyer goes off planet for “a vacation,” and comes back as Lord Dono Vorrutyer, and files a claim to his brother’s estate as eldest male heir. Mostly to block her cousin, a murderer and rapist, from taking it instead, but he ends up really enjoying being a guy and is married off to a young woman in a later book.
There’s also an entire subspecies of genetically engineered hermaphrodites, descendants of a failed social engineering experiment.
And a planet full of nothing but gay dudes.
I was afraid another world had been introduced and I’d missed it!! :eek:
Thanks for the answers everyone, I’ve read a few of those suggested but was unaware of quite a few others. 
I find the concept of physical transformation in general interesting, with changing sex being a subset of that, trust me its extremely hard to find stories about it which aren’t thinly veiled (if they are veiled at all) fantasies about power, domination, sadism and control over others. Personally I find it a rather unpleasant glimpse into the authors psyche. But there are some pretty good ones out there without this aspect.
Virginia Woolf (yeah, I know, not somebody you expect to be mentioned in a SF thread) wrote a curious novel called Orlando. In it, the main character Orlando changes gender. S/he also travels through time, so it’s sorta-kinda SF.
The most ancient character in fiction to have switched sexes is Tiresias, who figures in Greek myths.
This was actually made into a movie about 25 years ago, starring Tilda Swinton as Orlando.
Thank you, and regarding Tiresias, that reminds me of one of the rare decent amateur stories I mentioned called ‘Prisoners of Tiresias’ which had as its premise the exploration of a planet found through a dimensional transporter, this particular dimension having the quirk of switching people’s gender.
Be aware though if you go searching for it you’re going to come across a lot of fetishy weirdness, it also lays on the politics and social commentary a bit thick, but at least its a little more nuanced than most of its type.
Thank you! That was really annoying me.
PS Varley posted here at least once
http://boards.straightdope.com/sdmb/showthread.php?t=393697&highlight=Varley+sparky&page=2
In an example of using something without going into understanding it, I recall a made-for-TV SF thriller some time in the late 80s or early 90s, set in a Moon base, where one of the “twists” was figuring if the fugitive from Earth that was being sought had concealed his identity by having sex reassignment and becoming a her.