On April 26, 2001, about 1435 eastern daylight time, an Aerospatiale ATR 42-300, N223AT, registered to GPA ATR II, Inc., operated by American Eagle Airlines, as flight 5238, encountered severe to moderate turbulence during cruise flight over the Atlantic Ocean. Instrument meteorological conditions (IMC) prevailed at the time and an instrument flight rules (IFR) flight plan was filed for the 14 CFR Part 121 scheduled, international, passenger flight. The airplane was not damaged and there were no injuries to the captain, first officer, or nine passengers. The flight attendant sustained serious injuries. The flight originated about 1355, from the Georgetown Airport, Georgetown, Bahamas. The captain reported that while flying at 16,000 feet in visual flight rules conditions with scattered precipitation, air traffic control (ATC) advised of an area of turbulence that was located approximately 25 to 30 miles from their present position. The flightcrew was advised of a heading to fly which led the airplane into a cloud that was not depicted on the weather avoidance radar. "In this cloud we encountered moderate to severe turbulence...." According to the American Eagle Safety/Flight Service Trip Report (FSTR) which is an attachment to this report, "[flight attendant] Alvarez was finishing her beverage service and they hit turbulence. She flew into the air twice and cart came down on her right leg. She was on her way to the galley to stow cart." The captain also reported that the autopilot which was on at the time, did not disengage. A passenger who is an emergency medical technician (EMT), attended to the injured flight attendant and was assisted initially by the first officer. A medical emergency was declared and the flight continued to the destination airport and landed uneventfully. The first report to ATC occurred at 1448 local, when, while approaching the JUNUR intersection, a flightcrew member declared a medical emergency and advised the controller that the flight had encountered turbulence 50 miles back.