The invention is directed to a trocar seal adapted to form a seal around a surgical instrument, the trocar seal comprising a housing having an axis extending between a proximal end and a distal end and forming a working channel sized and configured to receive the surgical instrument; an elastomeric septum seal having a proximal face and a distal face, the septum seal being disposed in the housing and extending transverse to the axis of the housing across the working channel; portions of the septum seal defining a hole having a diameter less than or equal to the diameter of the surgical instrument so that during insertion of the instrument along the working channel the septum seal forms a seal with the instrument; and at least one structure formed integrally with or proximate to the septum seal to prevent inversion of the septum seal upon withdrawal of the surgical instrument. The septum seal or the housing may further comprise a sidewall to include the structure extending from the sidewall to the distal face of the seal to tether the seal distally. The structure may be integrally formed with the proximal face of the septum seal to reinforce the seal, or the structure may be integrally formed with the distal face of the septum seal to tether the seal distally. The structure may be an annular reinforcement or rib, and is formed so as to allow side-to-side movement or floatation of the seal. The trocar seal may further comprise a plurality of radially extending ribs formed on the proximal or distal face of the septum seal to reinforce the seal. The trocar seal may further comprise a tensile element formed on the distal face of the septum seal.