Several countries in the world, from Albania to China, experience unbalanced sex ratio at births. In Viet Nam, the phenomenon is very recent, but the increase measured since 2006 is extremely rapid. Currently, he national sex ratio at birth is almost 112 boys for 100 girls, and exceedes 120 in several provinces. This work is based on the comparison of two qualitative surveys, implemented in Hai Duong and Ninh Thuân provinces, in order to understand more about the root cause for son preference, and the different kinds of “pressure” within the family and the community, which lead some women to have sex-selective abortions. If the kinship system in Hai Duong province appears to be strongly patriarchal, hence the necessity to produce a male heir who will perform the ancestor’s worship and carry on the family name (SRB was 120.2 in 2009), we postulate that the situation in Ninh Thuân province is somewhat different (SRB was 110.8 in 2009).