A suture knot can be tied during a medical procedure by use of a suture retainer ring in connection with a suturing instrument. The retainer ring allows a user to orient a suture about the instrument, such that a knot in the suture is automatically advanced and tightened by withdrawing the instrument from a surgical site after placing the suture. The retainer ring can be an integral part of the suturing instrument, or it can be removably coupled to the suturing instrument to facilitate use of the retainer ring with other suturing instruments.