Power is at the core of feminist theories of sexual harassment, although it has rarely been measured directly in terms of workplace authority. Popular characterizations portray male supervisors harassing female subordinates, but power-threat theories suggest that women in authority may be more frequent targets. This article analyzes longitudinal survey data and qualitative interviews from the Youth Development Study to test this idea and to delineate why and how supervisory authority, gender nonconformity, and workplace sex ratios affect harassment. Relative to nonsupervisors, female supervisors are more likely to report harassing behaviors and to define their experiences as sexual harassment. Sexual harassment can serve as an equalizer against women in power, motivated more by control and domination than by sexual desire. Interviews point to social isolation as a mechanism linking harassment to gender nonconformity and women's authority, particularly in male-dominated work settings. (Contains 3 tables, 2 figures and 13 notes.)