A seal for a trocar sleeve comprises a sealing body which, in the direction of a longitudinal center axis of the sealing body, has a first axial end and a second axial end and, between said first and second ends, an elastic sealing element which, in a radially inner area relative to the longitudinal center axis, defines a passage for an instrument. Said sealing element has a substantially tubular hollow space whose radially inner wall area annularly surrounds the passage, and said hollow space contains a fluid and and has a radially inner wall area annularly surrounding the passage, and a radially outer wall area on a radially outer side of the hollow space, the radially outer wall area having a wall thickness larger than a wall thickness of the radially inner wall area.
