Aim: Adolescents in Vietnam have a low level of sexual activity, but this may increase with urbanisation and economic development. The aim of this analysis is to understand trends in correlates of permissive attitudes towards premarital sex among Vietnamese adolescents using an ecological framework. Methods: Data from the Survey Assessment of Vietnamese Youth from 2003 (n = 7584) and 2009 (n = 10 044) were analysed using multivariable logistic regressions to examine associations between permissive attitudes towards premarital sex and demographic and contextual factors among adolescents aged 14 to 25. Results: Correlates of having permissive attitudes towards premarital sex in both 2003 and 2009 included being male, older age, living in an urban area, living in the North, having ever used the Internet and perceiving that people in the community were having premarital sex. Variables that were significant in 2009 but not in 2003 included socio-economic status and belonging to an ethnic minority. Statistically significant changes in associations between 2003 and 2009 were observed for age, socio-economic status and belonging to an ethnic minority. Conclusions: The association of permissive attitudes with community norms and certain socio-demographic variables in conjunction with overarching economic development and urbanisation suggests that premarital sex will likely become increasingly common among Vietnamese adolescents. These trends should be further assessed as adolescent sexual activity becomes more common and adolescent friendly health services should be developed to provide appropriate and acceptable sexual and reproductive health care to young people.