The incident occurred on a scheduled flight from Brisbane, Australia to Singapore. The aircraft was in level flight at FL390, in the vicinity of airway intersection SABIL, when severe turbulence was experienced. In the passenger cabin a meal service was being carried out. Turbulence was not anticipated and the seat belt signs were off. The turbulence was of short duration, lasting for 15 seconds, but there were a number of injuries three serious and 24 minor. The aircraft commander decided to continue the flight to Singapore and made a request for medical services to meet the aircraft on arrival. The aircraft landed at Singapore 44 minutes later. An engineering inspection was carried out after landing and revealed no damage to the aircraft. The aircraft encountered turbulence probably associated with an area of rapidly developing CB cloud. Under the prevailing conditions of darkness weather detection and avoidance would have been achieved by reference to weather radar. Airborne weather radar is unable to detect rapidly rising cloud tops composed of small particles. The development of the cloud may have been at an early stage so that it was not detectable by radar although it was already visible on an infrared satellite image. It is known that severe turbulence can occur well above the tops of CB clouds.