A widespread outbreak of Hepatitis A occurred in Jefferson County, Kentucky. Illness was associated with eating at one of three restaurants. Case-control studies found that eating green salad was strongly associated with illness. Iceberg lettuce was considered the most probable vehicle of transmission. All three restaurants were supplied by the same fresh produce distributor. The investigation suggested that contamination occurred prior to receipt of the produce by the distributor. At that time, the lettuce was provided by four domestic suppliers. Just before the outbreak, these companies were receiving increased shipments of lettuce from Mexico. The exact farm origen of the lettuce was never determined.