Make it at least three.

"Don’t change [your company culture] by hiring or promoting just one woman, she’ll be isolated and surrounded by the status quo and will have to adapt to it, and she won’t be able to make a difference. Two women doesn’t work either. Make it at least three. Three or more women at the top of your creative department, on your management team, on your board begin to make a real difference and change the environment, the culture and the output.” 

 

Quote from an excellent article on Slate about companies trying to recruit women. What is your top tips? http://www.slate.com/blogs/xx_factor/2014/01/07/hiring_women_in_male_dominated_fields_companies_need_women_to_recruit_other.html