A multi-seal trocar system (10) includes a plurality of co-axial sealing elements (30 60,80) adapted for forming a seal with either a large or small instrument. Small and large scaling elements (45,62) are disposed in an in-line arrangement such that a single port is provided for instrument insertion. A zero seal (80) is disposed distally of the sealing elements to seal a working channel of the system and to prevent backflow when no instruments are inserted The small sealing element (45) is configured such that insertion of a large instrument automatically moves the small sealing element (45) out of its path, thereby avoiding contact with the large instrument