Plasma vitellogenin (VTG) concentrations and the presence of the ovo-testis (intersex) condition have been recorded in male flounder (Platichthys flesus) captured from several United Kingdom (UK) estuaries since 1996 as part of the endocrine disruption in the Marine Environment (EDMAR) project and earlier programs. It has been confirmed that plasma VTG concentrations in male flounder have remained elevated in several UK estuaries (e.g., Tees, Mersey, and Tyne) throughout the period covered by this study. However, the time-series data indicate that plasma VTG, a measure of environmental estrogen contamination, has decreased in fish captured from several estuaries, especially those of the Tyne and Mersey. Shorter time-series data sets from the Forth and Clyde estuaries also suggest a decrease in estrogen contamination at these sites. Trends associated with specific point sources of estrogenic contamination show site-specific patterns. For instance, plasma VTG levels in male flounder captured near the Howdon sewage treatment outfall (Tyne) have shown a steady decline to near baseline levels in 2001, while the plasma of male fish captured at a site adjacent to the Dabholm Gut discharge in the Tees estuary have shown little evidence of a sustained decline. The occurrence of the intersex condition was detected at a low but consistent prevalence through the study period, with the majority of cases recorded in fish captured from the Tyne and Mersey estuaries. The data set does not allow conclusions to be drawn about any temporal trends associated with this condition. The significance of the findings and possible mitigating influences are discussed in terms of the impacts on wild fish and the role of effluent treatment in reducing these.