The present invention relates to a trocar assembly comprising a cannula (40) and an obturator (1) arranged, in use, to be received within and extend through the cannula (4). The obturator (1) comprises a shaft (2) and a head (4). The shaft (2) is arranged to extend through the cannula (40) and having an external diameter which is less than the internal diameter of the cannula (40). The head (2) is arranged to protrude beyond the cannula (40). At least a portion of the head (4) has an external diameter which is greater than the internal diameter of the cannula (40). Said portion of the head (4) comprises a radially extending cut-out (18) such that the portion of the head (4) is radially collapsible for withdrawal through the cannula (40). The obturator (1) further comprises a locking member (30) which is received within the cut-out (18) to prevent withdrawal of the obturator (1).
