Ryanair flight FR4398, a Boeing 737-800, encountered turbulence on a flight between Dublin (Ireland) and Reus (Spain). When the aircraft was some 42 NM away from the city of Toulouse and on heading 138§, it made a right turn to heading 165§, direct to point PUMAL, which is near the border between France and Spain. On this segment the aircraft had to fly over the city of Toulouse. At 16:37:19, some 7 NM before reaching Toulouse, the crew initiated a turn to the right to try to avoid a storm cell that was developing over Toulouse. When they began the turn, the aircraft was at FL370 and flying at a speed of Mach 0.766. Its weight was 133,400 lb and the autopilot was engaged in lateral navigation (NAV) mode. The autothrottle was also engaged. The crew were unable to keep the aircraft from crossing the edge of the storm, which resulted in its being affected by the turbulent motions typical of these atmospheric phenomena. The turbulence lasted 29 s, starting at 16:38:11 and finishing at 16:38:40. As a result of the aircraft?s sudden movements, two passengers were hurt, one of them seriously,. Besides three cabin crew suffered minor injuries. The rest of the flight was uneventful and the aircraft landed at its destination airport normally. Causes/Contributing factors: The accident was caused when the aircraft entered a developing convective cloud that had not been detected by the crew. The severe turbulence associated with the cloud affected the aircraft, causing injuries to several passengers and crew who had not been alerted to the turbulence.