This study examined relations of multiple indicators of work identity and family identity with the number of weekly hours worked by 193 married business professionals. We found that men generally worked long hours regardless of the situational demands to work long hours and the strength of their work and family identities. Women's work hours, on the other hand, were associated with their work and family identities when weak situational demands permitted discretion over their work hours. We suggest that these sex differences can be explained by the ways in which women and men construe their work and family identities. (Contains 2 figures and 3 tables.)