A medical instrument positioner including a lever arm pivotally secured at a first end to a stationary base, which is preferably the base of a patient support such as an examination chair, and including a pole extending upwardly from a second end as well as a lockable caster secured to the second end for providing rolling but selectively lockable support of the positioner with respect to the base. The patient support provides a heavy, stable object for counteracting the moment created by, for example, a microscope and microscope mounting arm attached to the upper end of the vertical pole. The microscope mounting arm preferably takes the form of a linkage assembly secured to the upper end of the pole. The microscope mounting arm receives the microscope for allowing precise adjustment of the microscope orientation with respect to the patient.