This paper examines the puzzle of the recent rise in the sex ratio at birth in Viet Nam and relates its emergence to existing kinship systems and ethnic composition using 2009 census micro-data. We start with a presentation of the main socioeconomic and ethnic differentials in birth masculinity and stress the extent of regional variations. We then review the three intermediate factors leading to increases in birth masculinity: prenatal technology, declining fertility and gender bias. We use an indirect measurement of fertility behavior to demonstrate the close association between levels of sex ratio at birth and the intensity of son preference. Data on household composition indicate that Viet Nam is characterized by the co-existence of kinship patterns typical of East and Southeast Asia. We can then relate son preference in Viet Nam to the prevalence of more traditional patrilineal systems. The paper concludes with the implications of the cultural dimensions of prenatal sex selection on policy responses and the future change in the sex ratio at birth..
India, demography, population.