Objective: elaborate a scale for ageism in an organizational context (Escala de Ageismo no Contexto Organizacional or EACO), seeking evidence of its structural validity and investigating possible differences in prejudices against elderly workers. This article also highlighted differences between gender, age and levels of schooling. Method: the project was divided into two studies: the first focused on the construction of the EACO, testing the understanding of the initial instrument among 82 workers. A new version was sent to and analyzed by ten judges, resulting in a 28-item scale with six dimensions. The second study presented evidence of the validity of the EACO, using a more robust national sample. The modified instrument was electronically issued to 2,400 workers of varying ages from different regions of Brazil, with 600 participants responding. Results: Exploratory factorial analysis (EFA) resulted in an EACO with 14 items, with satisfactory eigenvalues, factorial loads and communality, grouped into two dimensions: D1 -negative attitudes, composed of cognitive and health aspects (α=0.83) and D2 -positive attitudes, composed of affective aspects (α=0.77). Younger workers had more negative attitudes towards aging than older workers, who in turn had more positive attitudes than younger individuals. Conclusion: The EACO tested ageism in organizations and demonstrated evidence of validity. It is also recommended, however, that the scale is used in its longer version in future research, with national and transnational groups and participants of different educational levels.