If they're from the same litter, it shouldn't matter.  If you get
young kittens at the same time I don't think it should matter either.
(In my experience.)  If you get two older cats, two males will fight
just as much as females will.  (Again, my experience.)

And have a great time with them.

Takayuki can tell you about adjustment problems of older cats.  (I
hope it's going better, Takayuki.)

Cantate

I'm a bit skeptical about the folk wisdom that says you shouldn't adopt
two cats of the same sex. (You've heard two males together is OK - I've
always heard that they should be opposite sex.) My personal experience
was that I adopted one female, and then a year later, another female, and
they got along fine. The second female was a kitten, though, so the older
girl maybe didn't see her as competition, or a threat, or whatever.

A few years later, I adopted a male - also a kitten - and he does not
get along with one of the girls. So, so much for the "opposite sex is
always better" theory. He gets along fine with my other girl, though.

I think that if they are two kittens, chances are they'll get along,
because they'll be growing up together. Kittens don't seem to be very
territorial toward other kittens or cats. If they're from the same litter,
so much the better - kittens from the same litter often seem to get very
close. So I think the age of the cats has a lot more impact than the sex.

But ultimately, I think it's really about personality. Some pairs of
cats just don't get along, or they take a lot more work to help them
tolerate each other. Just like people, some cats rub other cats the
wrong way, while others are best friends.

Good luck!

Joyce

I adopted a female cat and about 6 months later adopted another female. They
get along fine. They are not about 11 and 12 years old.

Almost 3 years age a rescued a mom and 3 kittens and kept one of the male
kittens.There was more of a problems with him wanting to play all the time
and the girls didn't .

If they are kittens I don't think the sex of the kittens should matter.

Ann

When you adopt them at the same time, I don't think it makes
much difference.  I had read that when you want to add a
second cat to a household, a kitten of the opposite sex from
your resident cat is best, but you can't prove it by me.

When Patches decided to adopt us, after three years as a
stray, my resident cat was another neutered male, and they
seemed to get along okay.

After Miu left us, I got Melisande (a female kitten) who
promptly fell in love with Patches - much to his chagrin.
(You never saw such a disgusted expression on a cat's face,
the first time he walked in the door after she arrived, to
be "assaulted" by an affectionate bitty!)  He never
attacked, although he did his best to avoid her at first,
but they became good friends.

After Patches succumbed to complications of skin cancer (a
white cat who had lived outdoors in the California sun for
several years), Melly and I were alone for about a year, but
she was clearly lonesome.  Then Cendrillon (another female)
joined us when my neighbor across the hall moved away and
abandoned her.  The two of them get along beautifully,
playing together, sometimes sharing my lap when I watch TV,
and often engaging in mutual grooming.

I think it has more to do with the personalities of the
individual cats you plan to adopt, than with their genders.
 (Although it would probably be easiest if they are
littermates, and already know each other.)

My first cat was a male. When I went to get another cat, I didn't
consider sex I considered age. I didn't want my older male to be
threatened by the newcomer, so I got a kitten. A couple of years later
when I wanted a new cat yet again, I once again went for a younger cat -
time it wasn't a bitty, but just a young 6 month old cat. Both of my
older ones then were boys. The oldest one would have nothing to do with
her (and only beat her up occasionally for fun) but my younger one who
was still more interested in play thought this was great. My youngest
one is a female.

To this day, my oldest cat (Tony) and youngest cat (Mattie) are not
friends. They can sleep in the same bed or occupy the same lap (with
great reluctance on Tony's part) but they rarely fight. Tony and the
middle cat, Stripey Thing, are buddies to the end. They groom each other
and sleep piled in a heap. Stripey Thing would sleep piled in a heap
with Mattie if Mattie would let him, but Mattie isn't interested - just
in playing together. I am the one she sleeps in a heap with.

They all have some strong personality traits that make it clear they
will get theirs. Mattie more than the other two I think. But they are
also laid back cats (luckily for me) I don't have turf wars. No one owns
certain territory or anything. And the adjustment period was nil. But I
got lucky. I don't know what I would have done with Tak's pair. He has
the patience of a saint.

In any event, I went with the age is important, not sex and ended up
okay. My crew are about as well balanced as three cats living in a small
apartment can be. Hope that helps.

Bridget