Because he absorbed a fatal dose of radiation.
The Tenth Doctor dies and regenerates into the Eleventh Doctor
The Tenth Doctor (a.k.a David Tennant) did not die. In fact, he regenerated into the Eleventh Doctor (a.k.a Matt Smith).
No, he is the tenth doctor in the series of doctor who.
he goes into a Radiation chamber or something to save donnas Grandad and dies... after that he goes and visits all his companions
He was exposed to a fatal amount of radiation after saving Wilf.
His very last words just before the tenth doctor regenerated was: "I don't want to go!"
The 10th doctor was played by David Tennant.
Doctor Who The Doctors Revisited - 2013 The Tenth Doctor 1-10 is rated/received certificates of: UK:PG
the 50th anniversary special
The sonic screwdrivers from the second doctor to the tenth doctor were made by the doctor himself but the eleventh doctor's sonic screwdriver was made by the tardis because the tenth doctor's sonic screwdriver wouldnt work.
The tenth Doctor's screwdriver is better
the name of the tenth doctor is david tennant .however this xmas in 2009 he will resign as the doctor and will be strongly missed and i myself am not watchin any other doctor who episodes that do not have david in them.the 11th doctor is going to be Matt smith.