Triclosan is a bactericide used in increasing shelflife of cosmetics, improving hygenics in sportswear as well as in toothpaste and in mouth wash. More than 350 tons Triclosan is annually produced in Europe, and most of it finally is emitted into wastewater at the end of its life cycle. Therefore, the fate of this compound in wastewater treatment is of high interest, especially as triclosan has detrimental effects on, e.g., micro-algae at very low concentrations. It has been demonstrated, that the elimination of triclosan is very effective in wastewater treatment with eliminination rates > 90%. However, a persistent transformation product (triclosan-methyl) is beeing formed in the activated sludge treatment process. In contrast to other studies, mass balances on wastewater treatment plants show that the fate of more than 50% of the incoming triclosan remains unknown.In this study we will present data on which part of the treatment process (BOD removal, nitrogen removal, phosphorus removal, i.e., aerobic-, nitrate reducing- and anaerobic conditions) is the most relevant for the elimination of triclosan as well as the formation of triclosan-methyl. Kinetic data for the different steps and conditions are being presented. Also we investigated the fate of the unknown mass fraction of triclosan in reactor experiments. Some results from full scale treatment plants will be given as well as first indications on how to decrease emissions of triclosan and triclosan-methyl in current wastewater treatment processes.