the invention provides a combination surgical trocar housing and selective reducer sleeve assembly in which the sleeve assembly members may be telescopically received within the trocar housing to reduce the diameter therethrough . the sleeve members provide a seal to prevent transmission of fluid within the annular area between internal and external diameters of respective members and may be latchingly secured relative to one another to resist telescopic expansive movement to stabilize the sleeve assembly relative to the trocar housing . the sleeve assembly permits acceptance through a single trocar housing of a number of auxiliary surgical instruments having serially smaller diameters , thus enabling performance of the surgical operation using each such instrument , without removal from the body wall of the original trocar housing .