Abstract: A closure system for a screw top container intended to contain a pharmaceutical or surgical medium comprises: a screw cap including a main body comprised of an annular wall with an internal thread for cooperating with an external thread adjacent an open end of the container, the body having a first open end for receiving the open end of the container and a second end closed by an end disc; a sealing formation within the main body for forming a seal with the open end of the container; and a tamper-evident band connected to the screw cap at the open end of the main body by at least one severable linkage, wherein the screw cap, sealing formation and tamper-evident band are integrally formed as a single unit for maintaining a hermetic seal with the container throughout a terminal sterilisation process.