What are the security implications for a population whose males, particularly those of the young adult population, significantly outnumber females?
But today, it no longer attracts as many sex-seekers as it once did.
Cheaper and more lax, neighbouring Cambodia is Asia's new temple of pleasure.
The transfers are made using "even more cruel and devious means than the original slave trade," Unicef's Kul Gautum told an International Symposium on Trafficking of Children, being held in Tokyo.
He said in Asia and the Pacific alone, more than 30 million children have been traded over the last three decades.
The high sex ratios in China and India in particular have implications for the long-term security of these nations and the Asian region more broadly.