REF:
http://www.straightdope.com/classics/a4_211.html
To see the answer, go to Google Images and search with the keywords:
Scotsman kilt Queen Elizabeth
On the first page expand the picture with rows of Scots Guards sitting with the Queen in the middle and inspect the men in the first row to the left.
Look… normally Cecil is the last word on everything, but this time he didn’t even bother to research well…
Kilts originally were worn with nothing underneath them because underwear hadn’t been invented yet… Indeed, as mentioned in the post, the closest thing to underwear was the fact that the scotsman’s shirt was a very long shirt that covered the area in question.
However, today’s modern kilt wearers, people who wear them every day or at least on a regular basis (of which I am proud to be one), wear a variety of things under their kilt. Some do keep it breezy, but many wear different types of under garments for a variety of reasons - an active lifestyle, being around children and/or animals, work regulations, and even comfort. Some wear undergarments on certain occasions and not on others. Some always wear something, and some never wear anything.
If you want to ask around, you should go to the places where the most frequent kilt wearers congregate. Try the following two sites:
and
Kilts Rock
ummm…
if the kilt-wearer is lucky, he wears a ribbon under the kilt =D
yum
As long as he’s got a sporran made out of a whole scooped-out badger, I don’t care what else he wears.
I think this question has just as much meaning as “what does a woman wear under her skirt?” Every kilt-wearer is different. For me, it depends on where I’ll be, who I’ll be with, and what I’ll be doing.
Believe me, when I’m emceeing an event, and I’ll be up on a stage with a bunch of little girls on the dance floor below me, I’m modestly covered underneath the kilt.
That picture seems to be AWOL. Can you provide a direct link?
Try here: Does Photo Show Queen Elizabeth II and a Colonel's 'Crown Jewels'? | Snopes.com
Two versions of the pic, one more, um, revealing than the other; Snopes thinks it’s not clear which one is authenic and which one has been modified. 
JRB
Thanks. I hope for his sake the second one is the fake.
I rather fancy Army Field Manual 7-22: Physical Fitness Training was intended, which shows up if you have “Scotsmen” instead of “Scotsman” in the search.
I can’t believe I’ll be the first to say,
No True Scotsman wears anything under his kilt!
My Dad was in the British Army in WW2, and his bunch shared a mess with a Highland regiment. The Highlanders were required, when in uniform, to be “regulation”, which is to say, wearing nothing under the kilt.
In the mess this was enforced by custom: anybody could flip up a kilt. If the wearer was not regulation, he had to buy everybody present a drink. If he WAS naked under the kilt, the flipper had to buy the round.
Ref: Scotsman and kilts, how do you make a Celtic cross?
Kick him in the bagpipes.
Providing something of a cite for pumpkinsparshott, from this article interviewing a Major of the Black Watch:
It’s my understanding – as a kilt wearer myself – that the regulations did allow for underwear to be worn when undertaking certain activities including participating in Highland games and dancing (and some form of marching that requires high-stepping).
Since the usual reason for donning my kilt is weddings and the like, and the chance that dancing may break out appears high, I feel that I can with good conscience meet the regulations. 
Although at one wedding (where the groom’s party and a number of guests were in kilts) we were encouraged to go commando and it would have been churlish to refuse. 
Nonsense. Are you saying this seriously, or doing a bit of satire?
I had thought long shirts to have been worn in medieval times (in Western Europe at least) as a form of undergarment, with the long back of the garment pulled forward and then the braies / hosen pulled up to keep things in place.
I’m not entirely sure how this worked with a plaid / great kilt (what with no hose and all)… but understand that that the shirt ends may have been knotted to form a breech clout of sorts.
For centuries, Scotsmen wore drawers (linen underwear) and hose, like most of the men in Europe. Kilts show up in the late 16th century, almost certainly with linen drawers underneath. The nonsense about going bare-assed under a kilt probably has a much more recent source. It’s no more an ancient Scots tradition than the Clan-linked tartans made up in the 18th century.
What does a Scotsman wear under his kilt?
…Why his boots of course!
Aren’t the ancient scots famous for being barelegged? And for their common dress (from the millennium to the advent of the great kilt) being a long shirt / tunic similar to the Irish léine, plus a mantle or brat?
(Excerpt from Early Highland Dress ).
And with the baggy léine phasing out in preference for a english style shirt. You may well be right about the linen undergarments, though I’ve not seen information either way on it. (But IANA costuming expert).
It’s perhaps a time-frame issue – the clan tartans are both 18th C and traditional… it just comes down to your definition of “traditional” and whether the custom needs to have 200, 500, or more years of history behind it.
Ring ding diddle diddle I de oh ring di diddly I oh!
gods I love that song! and yes, real men do wear kilts 