Michael gave 1,000 free tickets to the hospital as an expression of his gratitude for the excellent care he received when he was rushed there with pneumonia last November, the BBC said.
About 300 staff attended this week's concert at Wiener Stadthalle, but the rest of the tickets were sold with the singer's permission to raise money for lung disease research.
"This is one of the greatest honors of my life, to sing to the men and women who saved my life," the BBC reported Michael said.
The singer became ill last fall in Vienna just hours before he was due to perform. He was transported to the hospital where he was diagnosed with severe pneumonia and spent a month in the intensive care unit.