A trocar including a cannula with a tubular sleeve having a stepped region thereon is disclosed. The stepped region has a plurality of discrete steps. Each step has a step floor and a step support base tapering radially inwardly from the step floor to an adjacent step floor. When the trocar is inserted through the body wall, and the stepped region of the sleeve of the cannula contacts the body wall, the force required to inadvertently pull the cannula out of the body wall when surgical instruments are withdrawn from the cannula increases. Thus, the tubular sleeve of the cannula increases the retention force of the cannula during surgery. The retention force is increased without appreciably affecting the force required to insert the trocar through the body wall. Additionally, these benefits are achieved without using helical threads or externally mounted stability devices, which add cost, complexity and increased risk of causing unwanted tissue trauma.