The purpose of this study is explore and describe the expression of the sexual orientation in 232 Chilean adolescent (16 to 18 years old), resident of Santiago City and they were studying in high-school of middle socioeconomic level, these high-school are sex differentiated. Student responded a self-administrate Sexual Orientation Questionnaire created by Drs. Almonte - Herskovic. In this study were chosen variables associated to sexual orientation by many authors, these were: sexual identification, sexual attraction, sexual fantasies, feeling and romantics emotions and sexual behavior. The results indicated that 96,96% of males and 90,91% of females opted by heterosexual self identification, heterosexual was a mostly important tendency in all variables in both groups. Although, men and women were statically heterogeneous in the way that they expressed their sexual orientation, women presented more different options than men. Females responded non-heterosexuals options with major frequency than males. This paper postulated that could exist sexual dimorphism in the way that they express their sexual orientation and this dimorphism must be considerate in educative and clinical practice.