The aim of the present study was to develop and validate a short form of the Genderism and Transphobia Scale and assess adolescents' attitudes toward transpeople. A total of 800 Spanish adolescents aged between 14 and 18 years (50.70% girls, 49.30% boys) completed the Spanish version of the scale and other related questionnaires. The short form of the scale is composed of 12 items clustered into two factors (Transphobia/Genderism and Gender Bashing) that explain 54.22% of the variance. All the items showed good discriminating power, and the present scale demonstrated adequate reliability and validity. In the study, boys exhibited significantly more negative attitudes toward transpeople than girls did, both in the affective/cognitive dimension (Transphobia/Genderism) and in the behavioral dimension (Gender Bashing). Moreover, adolescents showed significantly more negative attitudes toward gender-nonconforming men than toward gender-nonconforming women. These results are discussed in terms of their relevance to the maintenance of discriminatory attitudes toward sexual diversity.