Will I stay or will I go?

We develop an integrated theory of the social identity mechanisms linking workgroup sex and race composition across levels with individual turnover. Building on social identity research, we theorize that social cohesion (Tyler, 1999; Hogg and Terry, 2000) and social comparison (Festinger, 1954) lead to well-known cooperative effects within subordinate-supervisor pairs of the same sex and race, but potentially competitive effects among demographically similar peers. Analyzing longitudinal human resource data on professionals employed in a large up-or-out knowledge organization, we assess the distinct effects of demographic match with superiors and demographic match with peers on the exit of junior professionals. We find largely cooperative effects of cross-level composition-junior professionals who work in groups with higher proportions of same sex senior professionals are less likely to exit. At the peer level, however, these effects are reversed, and professionals are more likely to leave as the proportions of same sex and race peers within the workgroup increase. The effects hold across demographic groups, but vary by majority/minority status, disproportionately affecting women and underrepresented minorities.