We investigate the role of workgroup gender and race composition on the career mobility of professionals in “up-or-out” organizations. We develop a nuanced perspective on the potential career mobility effects of workgroup demography by integrating the social identification processes of cohesion, competition, and comparison. Using five years of personnel data from a large law firm, we examine the influence of demographic match with workgroup superiors and workgroup peers on attorneys’ likelihood of turnover and promotion. Survival analyses reveal that higher proportions of same-sex superiors enhance junior professionals’ career mobility. On the flip side, we observe mobility costs accruing to professionals in workgroups with higher proportions of same-sex and same-race peers. Qualitative data offer insights into the social identification processes underlying demographic similarity effects on turnover and promotion in professional service organizations.