The gastropod Nassarius reticulatus has been used as a tributyltin (TBT) biomonitor over the last two decades, and it is now endorsed by Atlantic Europe environmental agencies. However, there is one important question debated by the earliest studies still unresolved, namely whether butyltin accumulation in tissues is sex-dependent or not. Thus, a field survey was conducted along the Cantabrian coast: samples were subject to both customary imposex and modern chemical analyses. No significant bioaccumulation differences between sexes were found for any of the three butyltin species examined (i.e. TBT plus derivatives di- and mono-butyltin). In addition, both lower-than-expected absolute butyltins and minor relative TBT proportions in tissues conform with decreasing pollution in nearby areas. Imposex, though, is generally still considerable due to a lesser responsiveness of population indexes. Finally, one sample showed no sign of imposex but quantifiable butyltins; these are good news indicating that TBT is getting back down to levels around the induction threshold of this specific biological effect.