Work uncertainty may affect gender disparities in professionals' upward mobility in organizational hierarchies. Professional work involves three forms of uncertainty--problem variability, strategic indeterminacy and dependence on autonomous actors--that weaken the association between performance and ability, leading organizational decision-makers to weigh gender more heavily in promotion decisions. Strategic indeterminacy also increases the need for trust, so decision-makers feel more comfortable promoting candidates of their own sex. These ideas are explored using data on promotions to partnership in U.S. law firms. Findings show that (1) promotions are less likely to go to women when work involves greater problem variability and strategic indeterminacy; and (2) the negative effect of strategic indeterminacy becomes stronger as the proportion of male partners increases. (Contains 2 tables, 2 figures, and 12 notes.)