The aim of this study was to examine changes in sexist attitudes and beliefs in a group of Spanish adolescents over a period of three consecutive years, with specific attention being paid to gender differences. Participants were 279 students (mean age at first assessment of 12.10years) who, in each of the three years, completed the Ambivalent Sexism Inventory and the Questionnaire on Attitudes towards Diversity and Violence. Longitudinal analysis showed that hostile sexism did not vary over time, whereas scores on benevolent sexism and on sexist beliefs and justification of violence all fell between the ages of 12 and 14, there being an equivalent decrease in boys and girls. Boys scored significantly higher than girls on hostile sexism, as well as on sexist beliefs. These results illustrate how sexist attitudes and beliefs change during adolescence and provide further confirmation that these variables show gender differences from an early age.