In the 1970s, the United States population experienced a notable drop in mortality rates, after several decades of relative stability. Has this increased longevity been enjoyed equally by males and females, so that sex mortality differentials are essentially the same as before? Or has one sex benefited more than the other? This paper focuses on the mortality experience of males and females between 1970 and 1977, by age and by leading causes of death. The 1970-1977 data are compared with two earlier periods (1920-1950 and 1950-1970) to show how recent trends contrast with previous ones. Overall, the recent data suggest a new situation for sex mortality differentials. In prior decades, females' longevity advantage over males increased. This continuing increase appeared for virtually all ages and leading causes. But in the 1970s, the increase slowed. Females' situation relative to males actually worsened for several age groups (under 1, 55-64) and for several leading causes (conditions of early infancy, bronchitis/empysema/asthma, homicide, peptic ulcer). Moreover, the pace of females' gains for heart diseases and cancer has slowed, and relative gains have stopped for cerebrovascular diseases and accidents. Reasons for recent changes in sex mortality differentials and possible future trends are discussed.