An infusion set assembly adapted to be secured to a skin surface, comprising: an infusion set including a fixed base member having longitudinally extending base members (87, 88), said fixed base member connectable to the skin surface; a movable slide member located inside the fixed base member having a needle or cannula connected thereto and movable relative to said fixed base member, said movable slide member being movable from a first position in which said needle or cannula is not exposed externally of said fixed base member to a second position in which said needle or cannula is exposed externally of said fixed base member; and an inserter comprising a fixed inserter member; a movable inserter member movably connected to said fixed inserter member and adapted to receive the infusion set; and locking feet (74, 75) that are configured to engage said longitudinally extending base members (87, 88), said inserter being connected to said infusion set for moving said movable slide member from said first position to said second position; wherein a flexible beam of said fixed inserter member extends rearwardly from a front wall of the fixed inserter member and engages ribs extending downwardly from said movable inserter member to prevent movement of said movable inserter member from a first inserter position that does not expose the needle or cannula to a second inserter position that externally exposes the needle or cannula; and said movable inserter member is only separable from the received infusion set when the movable inserter member is in said second inserter position. an infusion set including a fixed base member having longitudinally extending base members (87, 88), said fixed base member connectable to the skin surface; a movable slide member located inside the fixed base member having a needle or cannula connected thereto and movable relative to said fixed base member, said movable slide member being movable from a first position in which said needle or cannula is not exposed externally of said fixed base member to a second position in which said needle or cannula is exposed externally of said fixed base member; and an inserter comprising a fixed inserter member; a movable inserter member movably connected to said fixed inserter member and adapted to receive the infusion set; and locking feet (74, 75) that are configured to engage said longitudinally extending base members (87, 88), said inserter being connected to said infusion set for moving said movable slide member from said first position to said second position; wherein a flexible beam of said fixed inserter member extends rearwardly from a front wall of the fixed inserter member and engages ribs extending downwardly from said movable inserter member to prevent movement of said movable inserter member from a first inserter position that does not expose the needle or cannula to a second inserter position that externally exposes the needle or cannula; and said movable inserter member is only separable from the received infusion set when the movable inserter member is in said second inserter position. a fixed inserter member; a movable inserter member movably connected to said fixed inserter member and adapted to receive the infusion set; and locking feet (74, 75) that are configured to engage said longitudinally extending base members (87, 88), said inserter being connected to said infusion set for moving said movable slide member from said first position to said second position; wherein a flexible beam of said fixed inserter member extends rearwardly from a front wall of the fixed inserter member and engages ribs extending downwardly from said movable inserter member to prevent movement of said movable inserter member from a first inserter position that does not expose the needle or cannula to a second inserter position that externally exposes the needle or cannula; and said movable inserter member is only separable from the received infusion set when the movable inserter member is in said second inserter position. a flexible beam of said fixed inserter member extends rearwardly from a front wall of the fixed inserter member and engages ribs extending downwardly from said movable inserter member to prevent movement of said movable inserter member from a first inserter position that does not expose the needle or cannula to a second inserter position that externally exposes the needle or cannula; and said movable inserter member is only separable from the received infusion set when the movable inserter member is in said second inserter position.