Bush, 92, and his wife, Barbara, 91, were hospitalized for several days in January, causing the couple to miss the inauguration of Donald Trump in Washington.
The ailment Tuesday was the same as before: pneumonia. The 41st president's press office said that despite a mild case of the inflammatory lung condition, Bush was "in very good spirits and is being held for further observation while he regains his strength."
The president's press agent did not say how long Bush is expected to remain in the hospital. He is the oldest living president, though Jimmy Carter was born just a few months later in 1924.