The application relates to a two-part overlapping dressing for securing a cannula during intravenous catheterization on the skin surface of a patient. The dressing comprises a first flexible adhesive sheet (10) provided with an opening (16) spaced from all its peripheral edges； and a second flexible adhesive sheet (12). The opening (16) in the first sheet comprises a slit (18), one end of which terminates in an enlarged aperture (20). The second sheet (12) is dimensioned such that, when it is aligned with and adhered against the first sheet (10) in use, it is capable of overlapping the full length of the slit (18) so as to reduce the opening (16) to the size of the enlarged aperture (20). The apparatus allows for a more secure fitting of the cannula whilst minimising the risk of infection.
