Research-oriented medical school affiliates such as Siriraj, King Chulalongkorn Memorial and Ramathibodi Hospitals are among the largest in the country, and act as tertiary care centres, receiving referrals from distant parts of the country. Lately, especially in the private sector, there has been much growth in medical tourism, with hospitals such as Bumrungrad and Bangkok Hospital, among others, providing services specifically catering to foreigners. An estimated 200,000 medical tourists visited Thailand in 2011, making Bangkok the most popular global destination for medical tourism.