Shigella is a common cause of diarrhea in the United States, and accurate surveillance is needed to determine the burden of illness that they cause. Active surveillance for culture-confirmed Shigella infection was done as part of the Foodborne Diseases Active Surveillance Network (FoodNet). A total of 4317 cases of shigellosis were reported during 1996-1999 in the original FoodNet surveillance areas. The average annual incidence was 7.4 cases/100,000 population. The incidence was similar during 1996-1998, but it declined in 1999 to 5.0 cases/100,000 population. State-to-state variability was seen in the incidence of shigellosis. Higher incidence was observed in California and Georgia. Shigella sonnei accounted for 70% of the infections, followed by Shigella flexneri (24%). Compared with other age groups, the incidence was highest among children aged 1-4 years of (36.3 cases/100,000 population). Marked demographic differences were observed between infections with S. sonnei and S. flexneri.