This study examined the construct validity of the Direct & Indirect Aggression Scales (DIAS) (Finland: Abo Akademi University) [Björkqvist et al., 1992c] in 653 adolescents aged 14 to 17 in four Spanish high schools. This paper also examined sex and age differences in aggression. The factor structure of scales was assessed using exploratory factor analysis. Varimax rotation was used, with a factorial structure of three factors: physical aggression, verbal aggression and indirect aggression. The results showed that, compared with girls, boys reported a more frequent use of physical and verbal aggression. However, for indirect aggression no differences were found between boys and girls. A specific examination of sex differences on individual items of the DIAS showed that boys used physical, verbal and indirect aggression more often than girls. The findings also indicated that, as expected, adolescents in lower courses (14-15 years old) rated higher in all types of violence than adolescents in higher courses (16-17 years old). Also, we found that boys used physical and verbal aggression more often than girls did in all age groups studied. This study provided a better understanding of female aggression in the Spanish context and it enhanced our understanding of how aggression is expressed by Spanish girls. Aggr. Behav. 00:1–11, 2005. © 2005 Wiley-Liss, Inc.