The rise in China's sex ratio at birth during the last two decades has had a wide range of economic and social consequences, including excessive savings as families with boys compete to match their sons with girls who are scarce and rising rates of crime among the unmarried male population. These consequences are analysed using a global dynamic model that projects demographic behaviour and economic performance through to 2030. The results show that the proportion of unmatched unskilled Chinese men of reproductive age could be as high as one in four by that time. Policies to rebalance the sex ratio at birth will take decades to reduce the sex ratio at reproductive age and any associated allowance for higher fertility would slow growth in real per capita income. Yet our results suggest that more than offsetting gains could accrue from productivity improvements stemming from reduced crime.