Kosovo President Ibrahim Rugova says he has been diagnosed with lung cancer, but will not step down.
Mr Rugova is a veteran of Kosovo's drive for independence
Mr Rugova, looking weak and frail, said in a TV address to the people of the UN-run province he would have intensive treatment and "overcome this battle".
He will continue to seek his goal of independence from Serbia, he said.
Mr Rugova, regarded as a moderate ethnic Albanian and re-elected last October, was reported to have fallen ill with flu last week.
He cancelled some engagements, and spent several days at the US military medical centre in Landstuhl, Germany.
"Doctors have found that I suffer from a localised lung cancer and they have assigned me an intensive healing therapy," he said.
"I am convinced that with the help of God I will overcome this battle."
Kosovo has been under UN administration since 1999, when a Nato bombing campaign against Serbia stopped Serb forces expelling the ethnic-Albanian majority during an Albanian separatist insurgency.
Mr Rugova led passive resistance to Serbian rule in the 1990s.
Correspondents say his illness could endanger talks planned for later this year on the province's future status.
The minority Serb population is bitterly opposed to independence.