An injector device assembly including: a subcutaneous infusion set including a cannula (26, 126, 226) for the delivery of medication or medical fluids; and an injector device (10, 110, 210) including: an injector device housing (28, 128, 228); a releasable cover (42, 142, 227); a plunger (30, 130, 230) with a medical insertion needle (12, 112, 212) for transcutaneous placement of said cannula (26, 126, 226), wherein said insertion needle (12, 112, 212) extends through said subcutaneous infusion set (14, 114, 214) and protrudes from the end of said cannula (26, 126, 226), wherein said injector device (10, 110, 210) is designed for transcutaneous insertion of said cannula (26, 126, 226) with said insertion needle (12, 112, 212) extending there-through, being removable from said subcutaneous infusion set (14, 114, 214) while maintaining the transcutaneous placement of the cannula (26, 126, 226), characterised in that said injector device housing (28, 128, 228) has a nose end accommodating movement of the subcutaneous infusion set between a retracted position disposed substantially at a rearward end of the device housing (28, 128, 228) and an advanced position, wherein said releasable cover (42, 142, 227) is secured to said nose end of said injector device housing (28, 128, 228) when the subcutaneous infusion set is in said retracted position, the releasable cover (42, 142, 227) covering said subcutaneous infusion set (14, 114, 214), whereby said injector device (10, 110, 210) with said releasable cover (42, 142, 227) secured to walls of said injector device housing (28, 128, 228) substantially defines a closed housing for said subcutaneous infusion set (14, 114, 214); and wherein said injector device assembly preferably being a sterile sealed, single use assembly. a subcutaneous infusion set including a cannula (26, 126, 226) for the delivery of medication or medical fluids; and an injector device (10, 110, 210) including: an injector device housing (28, 128, 228); a releasable cover (42, 142, 227); a plunger (30, 130, 230) with a medical insertion needle (12, 112, 212) for transcutaneous placement of said cannula (26, 126, 226), wherein said insertion needle (12, 112, 212) extends through said subcutaneous infusion set (14, 114, 214) and protrudes from the end of said cannula (26, 126, 226), an injector device housing (28, 128, 228); a releasable cover (42, 142, 227); a plunger (30, 130, 230) with a medical insertion needle (12, 112, 212) for transcutaneous placement of said cannula (26, 126, 226), wherein said insertion needle (12, 112, 212) extends through said subcutaneous infusion set (14, 114, 214) and protrudes from the end of said cannula (26, 126, 226), wherein said injector device (10, 110, 210) is designed for transcutaneous insertion of said cannula (26, 126, 226) with said insertion needle (12, 112, 212) extending there-through, being removable from said subcutaneous infusion set (14, 114, 214) while maintaining the transcutaneous placement of the cannula (26, 126, 226), characterised in that said injector device housing (28, 128, 228) has a nose end accommodating movement of the subcutaneous infusion set between a retracted position disposed substantially at a rearward end of the device housing (28, 128, 228) and an advanced position, wherein said releasable cover (42, 142, 227) is secured to said nose end of said injector device housing (28, 128, 228) when the subcutaneous infusion set is in said retracted position, the releasable cover (42, 142, 227) covering said subcutaneous infusion set (14, 114, 214), whereby said injector device (10, 110, 210) with said releasable cover (42, 142, 227) secured to walls of said injector device housing (28, 128, 228) substantially defines a closed housing for said subcutaneous infusion set (14, 114, 214); and wherein said injector device assembly preferably being a sterile sealed, single use assembly.