Koch looked jovial as he spoke briefly Monday outside NewYork-Presbyterian Hospital. He was admitted last week with pneumonia and flu.
He said he planned to go to his office briefly, then do some reading at home.
On Friday, Koch said through a spokesman that he was looking forward to celebrating his 88th birthday this Wednesday. He'll be at an annual reunion with members of his administration at Gracie Mansion, the official mayor's residence.
Koch also was hospitalized with anemia in September.
Koch served three terms from 1978 to 1989. The Democrat is famous for asking constituents, "How'm I doing?"
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