A safety device (10) for a medical needle (11) has a sleeve (28) defining an internally tapering forward portion (30) and a needle carrier (14) located within the sleeve (28) for axial movement relative to the forward portion (30). A locking member (23) is mounted on the needle carrier (14) and has a plurality of resiliently deformable fingers (25) bearing on the internal surface of the sleeve and slidable along the tapering forward portion (30) as the carrier moves relative thereto, so as to impart a force between the carrier (14) and forward portion (30) to restore those components to their initial position. A cam arrangement (33) turns the locking member (23) following initial axial movement between the carrier (14) and forward portion (30) so that the forward ends of the fingers drop behind abutments (35) provided at the rearward end of the forward portion, upon the carrier and forward portion returning to their initial positions. This then blocks further axial movement between those components (14, 30).