Vast majority of mathematicians are male and this situation hasn't changed for centuries. And exceptions like Hypatia of Alexandria (ca. 400 AD) only affirm the rule. This situation was connected with the fact, that women didn't have access to higher education. But even as women liberation began most of the women were not eager to study mathematics.
That has changed since World War II, when more girls could get higher education and governments began encouraging women to study mathematics, natural sciences and other subjects, that were thought to be too complicated for women. Nowadays The Association for Women in Mathematics's aim os to support women to build careers in mathematics. This organisation works for equal eduction and work opportunities for women in the field of mathematics.
But in spite of all the obstacles talented female mathematicians like Rózsa Péter (1905–1977), Julia Robinson (1919–1985), Olga Taussky-Todd (1906–1995), Émilie du Châtelet (1706–1749), and Mary Cartwright (1900–1998), Ada Lovelace (1815–1852), Maria Gaetana Agnesi (1718–1799), Emmy Noether (1882–1935), Sophie Germain (1776–1831), Sofia Kovalevskaya (1850–1891) studied maths.