© 2015 American Psychological Association. Presenteeism (showing up for work while sick) is detrimental for employee productivity, yet little is known about its impact on coworkers. Presenteeism may be particularly important when considering coworker reactions that may depend on how similar the sick person is to the coworker. The black sheep hypothesis suggests that the detrimental effects of coworker presenteeism on emotional and behavioral reactions will be exacerbated when there is greater demographic similarity to the perpetrator because the violation of norms of reciprocity, empathy, and concern for others' well-being reflects negatively on one's in-group. We tested the black sheep hypothesis in 2 samples: (a) 81 short-term teams (N = 254) where we manipulated presenteeism using confederates who acted as either sick or healthy coworkers and (b) 34 student project teams (N = 104) that collaborated for 3 months and we measured coworker presenteeism. Across the studies, mediated moderation results yielded some support for the black sheep hypothesis. When they were of the same race or sex, coworker presenteeism led participants to feel less positively and exhibit lower physical engagement and more organizational deviance (Study 1). When coworkers were more racially similar to the participant, coworker presenteeism triggered fear of contagion and negative affect resulting in more organizational and interpersonal deviance (Study 2).