A solar still was employed for the dewatering of olive mill wastewater over a series of consecutive days. The collected distillate and the remaining pulp were analyzed to test the method for treating agro-food industry wastewater. The efficiency of solar distillation of olive mill wastewaters was examined. Due to reduced energy consumption and relatively high temperatures achieved in the still, solar distillation could be applied in any process where separation of liquid and solid phase is required. A quantity of olive mill wastewater was left inside the solar still for 9 days, under outdoor conditions. Critical quality parameters (e.g. chemical oxygen demand, pH, total and volatile solids, total Kjeldahl nitrogen) were determined by daily sampling of both the distillate and the basin liquid. In addition, solar radiation and liquid, glass and ambient temperatures were recorded. It was shown that the distillate produced was free from solids, 80% lower in terms of COD and 90% in terms of TKN, while the basin residual was in solid form with only 15% water concentration and without any odor emissions. (C) 2003 Published by Elsevier Ltd.