A positioning device for screws used to fasten an endomedullary nail (2) having a principal direction of extension (A2) and presenting at least one hole (DH1, DH2) for the passage of the screws, comprises an arm (5) which is connectable to the nail (2), a bar (6) mounted at a first end of it (6a) to the arm (5) and extending substantially parallel to the principal direction of extension (A2) of the nail (2), an alignment head (7) mounted in the vicinity of a second end (6b) of the bar (6) opposite the first end (6a), the head (7) being made at least partly of a radio-transparent material, having at least one hole (13, 13', 14, 14') for guiding the fastening screws and being movable relative to the nail (2) through the agency of respective adjustment means (8) in order to bring the at least one guide hole (13, 13', 14, 14') into alignment with the at least one passage hole (DH1, DH2).
