Imposex was quantified in Stramonita haemastoma from the Bizerta Channel during a one-year study period and the effect of gastropod size and shell fouling by epibiotic barnacles investigated. Butyltin concentrations (tributyltin (TBT) and its 15 derivatives di-and mono-butyltin) were also investigated in the soft tissue of the gastropods to depict temporal trends in pollution. Kelibia beach was chosen as a reference site (not polluted by organotin) to depict whether barnacle fouling could intervene in imposex development. Imposex incidence in the Bizerta Channel was greater in females fouled by epibiotic barnacles compared to non-fouled females. Considering the size of gastropods, large females (fouled and non-fouled) always exhibit higher imposex indices than smaller females. The concentrations of organotin compounds were found to be similar 20 in the studied species, independent of sex or fouling condition. For Kelibia beach, no imposex was recorded in fouled and non-fouled snails, while butyltins were below the limit of detection. Results gathered in the present study confirm the effect of size and epibiotic barnacles as factors affecting imposex quantification in gastropods. The absence of imposex for Kelibia beach suggest that barnacles do not promote the development of imposex, but could be a secondary factor amplifying the effect of imposex. Furthermore, this investigation showed a significant decrease in imposex and TBT levels in Bizerta 25 Channel as compared to previous work reflecting the effectiveness of a TBT ban on a global scale.