A disposable guide device for spinal surgery comprises two tubular guide bodies extending along respective main axes between a proximal end and a distal end to guide a surgical operation on a vertebra of a patient, a plurality of support feet projecting laterally relative to each guide body, near said proximal end, each defining a contact area configured to abut on a side of the spinous process or on a lamina or facet or transverse process of the vertebra of the patient, in a mating configuration, at least one junction element extending between the guide bodies, starting from the respective distal ends, in order to space them from each other, wherein the guide bodies are oriented so that the proximal ends are more distant from each other with respect to the distal ends.