High sex ratio at birth due to son preference has been known in China historically, but it was thought this phenomenon would diminish with modernisation. The aim of this study was to investigate abortion decisions and reported sex ratios at birth in the context of successive family planning policies in Huaning County, Yunnan Province, in China. Abortion patterns and reported sex ratios at birth of a random sample of 1,336 women aged 15-64 were analysed for the period 1980--2000, in relation to parity and sex of previous children. There was a mole bias in the abortion pattern during the 1980s, but by the end of the 1990s most pregnancies of women with two children were being terminated. Sex ratio at birth rose from 107 in 1984--87 to 110 between 1988--2000 in Huaning. While women's reproductive decisions were influenced by son preference over the whole period, the means used to ensure a son differed with changing family planning policies. We conclude that rising sex ratios in the context of falling fertility and modernisation is an alarming socio-demographic issue, which defies historical experience. Assumptions that discrimination against girls would diminish with economic development and female education have proven simplistic. Action is urgently needed to reduce and mitigate the effects of discrimination against girls.