In this study we present the results of an intersex survey of Littorina littorea along the heavily polluted Western Scheldt estuary (the Netherlands), and record for the first time the intersex phenomenon in L. littorea from Dutch waters. Intersex differed significantly between localities and was the highest in the vicinity of the harbours of Antwerp and Vlissingen, as reflected by the ISI distribution along the estuary. In contrast, sterility did not differ significantly between the different sites, but nonetheless, followed the ISI distribution as well, ranging from 0 to 33\%. Despite the current ISI levels are high (maximum=1.26), they are still much lower than the ISI levels reported for L. littorea in some German harbour areas. Copyright © 2001 Elsevier Science Ltd.