Why do you think you're the only woman?
Because I am 
Construction is very white male dominated. There's no ethnic minorities either at my place and no (openly) homosexual men either. When our gender report was produced it specified only 1.8% female in a staff of over 6000. I do quite a bit to encourage young people into the industry and especially like to work with young women. I'm a firm believer in the right person for the right role and I think the industry doesn't traditionally attract minorities because of a "macho" perception but it's really an exciting industry with great opportunities.
Is the atmosphere different?
Yes it is really, it's all pretty schoolboy humour. Sometimes I miss having a really close female work friend to identify with.
Are you treated differently or feel that your colleagues change their behaviour when you're around?
Some do, some don't. I'm definitely not seen as "one of the boys" and don't want to be. But then I'm not seen as a wilting wallflower either. Some will apologise if the language or subject matter is particularly crass, most won't, which is fine. Most will temper racist or homophobic language, or particularly objective or derogatory comments about women around me because they know I won't tolerate it and will call them out on it.
Are your colleagues sexist/have you experienced sexism?
Yes, they are in their language, but a lot of that is just for show. They know I'm good at my job, don't expect to be treated differently and I do believe I'm respected. I don't feel that I've been adversely affected really, which is good. I don't play golf, which is still where a lot of deals are done, and so am excluded from that aspect which is a big one, however that's my choice really, there's no reason why I couldn't take some lessons and join in. Sexism along the lines of "I'm interviewing admin today, let's see who's got the biggest tits and employ her" (actual comment) is very very common, though is for show really and wouldn't actually be acted on. Some men think it's funny, some don't like it, I always call it out but never take it further and report it, though I think I might if it was something I felt very serious or true.
That said, I've been hit on a number of times, had trousers dropped in front of me, had many comments about my appearance, sex life etc etc but I've never felt really threatened or unsafe.
@Want2bSupermum
Your experiences are really interesting to read, especially with regard to the differences between the UK and the US. I do think that a large part of the situation with me is related to the the fact that there is still an overriding perception in the industry that women should be at home. Most of the blokes wives are stay at home mums or mums with jobs that work around the kids (dinner ladies, parttime admin etc) and so when I'm dashing off to get the kids or working in the holidays or on nights I get a few comments about not being with the kids, even had one asking why I'd bothered to have kids if I didn't want to spend any time with them
. Seeing as he had kids too I threw the question right back at him 