This paper describes the performance of a directly heated solar desalination system. The design concept is based on using a direct solar energy collection unit, integrated with flash evaporation and low temperature multi-effect distillation (LT-MED) equipment. Key parameters affecting desalination rate include flashing evaporation pressure, first effect distillation pressure and seawater temperature. The experimental results indicate that at flash evaporation pressure of 0.01 MPa, first effect distillation pressure of 0.004 MPa, and the temperature of solar-heated seawater of 78 degrees C, the system can reach steady state operation in 17 min. At steady state, desalination rate of 0.204 x 10(-3) m(3)/min is obtained. On raising temperature from 70 to 78 degrees C, net increase in desalination rate of 0.165 x 10(-3) m(3)/min is achieved. In contrast, the change of first effect distillation pressure only had minimum effect on desalination rate. Experimental results are in agreement with the theoretical analysis. If temperature continues to increase beyond 78 degrees C, scaling due to precipitation of CaSO(4) takes place. In this study, the techniques that prevent the system from scaling deposits are discussed. (C) 2009 Elsevier Ltd. All rights reserved.