Wind energy conversion systems have been receiving increasing attention in recent years, particularly in remote areas, where power from the utility is not available or is costly to install. Among many applications, wind electrical systems are successfully used for pumping water. Owing to the non-linear characteristics of these systems, their control is essential to attain high efficiency. In this work, concepts of sliding mode control are employed to guarantee global stability and to optimize the efficiency of a wind electrical water-pumping system. The measurement of wind speed is avoided. A thorough analysis of stability and dynamic behaviour is realized. Simulation results are presented. Copyright © 2003 John Wiley & Sons, Ltd.