An articulation mechanism for use with a surgical apparatus having an articulating tool assembly is described. The articulation mechanism includes a rotatable shaft which is fixedly secured to a disk defining a spiral groove or slot. A linearly movable translation member is provided and includes a pin which is received within the spiral groove such that rotation of the disk effects linear translation of the translation member. The configuration of the spiral groove can be selected to provide any desired ratio of angular rotation of the disk to linear advancement of the translation member. As such, the configuration of the spiral slot can be selected to provide a uniform rate of articulation of the tool assembly of the surgical apparatus or a variable rate of articulation.