Click here for the most recent update on U.S. Senator Mark Kirk's condition.
Sen. Kirk suffered a stroke and underwent surgery on January 23 to relieve swelling around his brain.
The 51-year-old Kirk checked himself into Lake Forest Hospital in Illinois. He was later transferred to Northwestern Memorial Hospital in Chicago, where tests showed that he had suffered a stroke.
A statement from Kirk's office said the surgery was successful and that doctors are "very confident" in his recovery based on his age and health.
Kirk was elected to the Senate in 2010, winning the seat formerly held by President Barack Obama .