We examine trends in premarital sexual behavior in the Red River Delta and Ho Chi Minh city and surrounding environs in Vietnam using data collected in 2003-2004 from men and women married during three different periods in Vietnamese history. We also describe levels of premarital sex by type of sexual partner (spouse or non-spouse) and with whom individuals first have sex. The recent increases in premarital sex among men in the Red River Delta have led to convergence in the levels of premarital sex between northern and southern Vietnam, although there are important regional differences in whether men have sex before marriage with someone other than their future wife. Women are considerably less likely to report having had premarital sex than men. The findings are compared to those from other recent surveys conducted in Vietnam, and their implications for the spread of the HIV/AIDS epidemic and the measurement of related behaviors in surveys are considered.