Evaluation of the industrial pretreatment plants in Istanbul Metropolitan area is presented. Out of 7899 industries located in Istanbul, 1420 of them require pretreatment to meet the discharge criteria. Currently, there are 532 pretreatment works which treat 82.6 percent of the industrial wastewaters. Discharge standards and the compliance monitoring system for the industrial wastewater discharges into the public sewers as applied by the Istanbul Water and Sewerage Administration are discussed. The performance data of the pretreatment plants are given based on the percent non-compliance and percent removal efficiency figures determined for different categories of industry. Problem areas in terms of industrial sector and in terms of quality parameters are identified. (C) 1997 IAWQ. Published by Elsevier Science Ltd.