There's provided a flip-top cannula assembly including a cannula having a cannula seal for receiving a range of surgical instruments having a first predetermined diameter and a reducer cap movably mounted on the cannula. The reducer cap includes a reducer seal having an opening which is substantially smaller than that of a cannula seal associated with the cannula for receiving a range of surgical instruments having a diameter smaller than that of the first predetermined diameter. In the disclosed embodiments, the reducer seal is movable from a closed position wherein the reducer seal overlies the cannula seal to effectively reduce the seal opening of the cannula to a closed position wherein the reducer seal is spaced apart from the cannula seal.