On May 25, 1999, about 1630, eastern daylight time, a Boeing 737, N16703, operated by Continental Airlines as flight 236, encountered turbulence while descending for landing near Newark, New Jersey. The airplane was not damaged. Two flight crewmembers, 6 flight attendants, and 68 passengers were not injured. One flight attendant sustained a serious injury to his ankle. Visual meteorological conditions prevailed, and an instrument flight rules flight plan was filed for the scheduled passenger flight that departed Mexico City, Mexico, destined for Newark, New Jersey. The flight was conducted under 14 CFR Part 121. According to the captain, while descending through 10,000 feet msl, and traveling in and out of cumulus clouds, the airplane experiences "lite" turbulence. While the fasten seatbelt sign was on, the airplane then experienced an "abrupt" vertical jolt. "Shortly after", a flight attendant called from the aft galley, and advised the flight crew that a flight attendant was injured during the encounter. A doctor onboard the flight advised the crew that the flight attendant "probably" broke his ankle. The flight attendant was placed in a passenger seat, and ice was applied to the injury. The captain instructed a dead heading flight attendant to assume the injured flight attendants duties, and requested priority from approach control because of a medical emergency. After landing, the injured flight attendant was removed, and transported to a local hospital for x-rays. In the NTSB Form 6120.1/2 the operator stated that the flight attendant fractured his right tibia and fibula leg bones.