Applying social identity theory and the relational demography approach, this paper proposes that the effect of age diversity on individual team members' health is contingent on the individual age as well as on age stereotypes. We suggest that younger and older employees' health is negatively associated with age diversity, while middle-aged team members' health is not affected. We further postulate that age stereotypes strengthen the negative effect of age diversity for the younger age group, while they weaken the effect for older employees. For middle-aged team members, age stereotypes are expected not to determine the relationship between age diversity and health. We tested our hypotheses based on data from a representative sample of the German workforce (n=1,214). The results fully confirmed our hypotheses.