Three flight attendants aboard United Airlines Flight 650 were taken to Resurrection Medical Center and Advocate Lutheran General Hospital in Park Ridge, Ill., after the plane landed at O'Hare International Airport about 12:30 p.m. after a flight from Santa Ana, Calif.
The Boeing 757 was carrying 146 passengers and eight crewmembers.
"It was unexpected turbulence over northern Missouri as the aircraft was preparing for descent into Chicago," said United spokesman Jeff Green. "The seatbelt sign was on."
A Fire Department spokesman told WBBM-AM, Chicago, the flight attendants suffered bumps and bruises. Three people declined treatment at the airport.
United said no passengers were injured.