Abstract Torsional vibrations are detrimental to the life of drillstring components (1,2,3,4). Although methods of controlling them have been proposed (1,3,4), their general dependence on strain gauges to measure drillstring torque make them unsuitable for the drilling environment. In this paper we describe a new, practical, system which does not use such a sensor, and present extensive field test results taken from a semisubmersible rig drilling in the North Sea. The system was shown to be very effective in suppressing torsional vibrations. It uses measurements of motor current, acceleration and a microprocessor to modulate the drive to the motor. An analysis is given to show that not only does the system performs just as well as one using a strain gauges sensor, but it also performs better than a system which uses motor current only. Considerations for the system design are also discussed. A significant reduction of drillstring torsional vibrations, DTV's, will reduce the cost of drilling wells by reducing damage to drillstring components and lost rig time. Drilling efficiency is enhanced through the suppression of "stick-slip" motion at the bit.