Ashlee Simpson collapsed following a performance in Tokyo yesterday (Dec. 15) and has been hospitalized. The 21-year-old singer had just performed her single, "Boyfriend" for MTV Japan, when she told the audience she felt sick. She then collapsed in an elevator and was rushed by ambulance to a hospital.

Simpson's spokesperson would not give further details or provide her condition. The artist's Monday appearance at the Radio Music Awards has been canceled.

Simpson has been touring to support her sophomore Geffen album, "I Am Me," which debuted at No. 1 on The Billboard 200.