Gender diversity on the Boards of Directors has become an important topic in the field of corporate governance. According to this study, only 6.61% of the directors in the top 1,085 Spanish companies are women. To identify the causes and possible types of discrimination behind this low level of female representation is a key issue, because they will have different economic implications. Some signs of discrimination have been found when the proportion of women on the board is estimated with count data models. The proportion of women is higher when there are more available positions representing shareholders. There are clubby companies in which the homogeneity of the board prevails. Finally, there could be companies that systematically underestimate the abilities of women, a situation that tends to disappear when the companies already have female directors.

Key words: gender discrimination, corporate governance, Board of Directors, glass ceiling.
JEL Classification: G34, J16, M14, C35.