Seven hundred and six specimens of Scolelepis cf. chilensis and 551 specimens of Scolelepis goodbodyi were analysed. Individuals of each species were classified according to sex (male, female, and immature individuals). Width (w) and height (h) of setigers 3 and 5, the position of the first and the last gametogenic setigers, the total number of setigers, and the total length of each worm were measured. The area and volume of the setigers were estimated. Discriminant analysis was used to determine whether there were sexually dimorphic features, apart from the presence of gametes. Linear regression analysis was used to evaluate the relationship between each parameter and the number of setigers. Scolelepis cf. chilensis was found to be significantly larger than S.goodbodyi (t=21·71 and t=36·44, P<0·05 for length and number of setigers, respectively). These species also differed in the position of the first gametogenic setiger, which averaged 27 (SD=3) in S. cf. chilensis and 22 (SD=1) in S.goodbodyi (t= 29·18, P<0·05). There were no sexually dimorphic features in either sex of S. cf. chilensis (Wilks' lambda=0·9675, P>0·05, eigenvalue=0·034) or S.goodbodyi (Wilks' lambda=0·8429, P>0·05, eigenvalue=0·186). The total length showed the strongest correlation with the number of setigers in both species (r2=0·887 and 0·850 for S. cf. chilensis and S.goodbodyi, respectively), followed by the width and the volume of setigers.