Guttentag and Secord (1983) hypothesize that sex ratios (the number of men per 100 women) affect the roles of both men and women. They suggest that although high sex ratios decrease men 3 dyadic power, when sex ratios are high men use their structural power to control women. Their theory can be combined with the routine activities approach of Cohen and Felson (1979) or with a version of the power-threat/power-competition hypothesis of Blalock (1967) to develop a power-control theory dealing with the relationship between sex ratios and rape rates: i.e., when sex ratios are high, rape rates should be relatively low. Analyses of data from the United States for the years 1962, 1967, 1972, 1977, 1982, and 1987 support this hypothesis.