Influenza activity in the United States continued to increase during December 14-20, 2003. The proportion of patient visits to sentinel providers for influenza-like illness (ILI) overall was 7.7%, which is above the national baseline of 2.5%. Influenza activity was reported as widespread by health departments in 45 states, New York City, and the District of Columbia; four states reported regional influenza activity; and one state reported local influenza activity.