Imposex levels in Nassarius reticulatus (L.) were determined in 44 sites along the Portuguese coast in 2006 in order to describe spatial and temporal trends of TBT pollution in the area. The percentage of females with imposex across sites varied between 20 and 100, denoting the extent of this phenomenon throughout the Portuguese coast. The mean female penis length per site varied between 0.0-8.0 mm and the relative penis length index (mean female penis length x 100/mean male penis length) attained a maximum value of 92%, i.e., female penis never surpasses the size of the male penis but nevertheless it can almost approach the male dimensions. The vas deferens sequence index ranged from 0.2 to 4.5 and the oviduct convolution index varied between 0.0 and 1.3 across stations. The penis growth, the vas deferens development and the oviduct convolution were all correlated and constitute visible signs of a global virilisation progression in females in response to the proximity of harbours that constitute the main TBT pollution sources. The results indicate that about 95% of the surveyed sites were still exposed to TBT water concentrations above the OSPAR Environmental Assessment Criteria. Nevertheless, signs of recovery are shown by the significant reduction of VDSI levels in 2006 in comparison to 2003, which points to the efficacy of the EC Regulation 782/2003 in reducing TBT pollution levels in the Portuguese coast.