How does social context influence the similarity effects on organizational attachment? Using self-categorization theory, similarity attraction theory and social identity theory as the theoretical underpinning, I explore the research question in the formal work group and the organizational reference group, two different conceptualizations of social context. Contrary to predictions, no significant similarity effects were found in either context. In testing a revised model in which communication is a partial mediator between similarity and organizational attachment, however, I find that organizational reference group similarity in gender, ethnicity and organizational tenure significantly predict organizational attachment. In particular, similarity in ethnicity negatively predicts job satisfaction, one measure of organizational attachment. Such results show that a direct positive similarity effect may be too simplistic to capture the nuances in people’s psychological and behavioral reactions to demographic similarity.