In an MR guided surgical system which is carried out in the bore of an MR magnet, there is provided a microscope system for viewing the required part of a patient which includes stereoscopic viewing components arranged for use in generating 2D and 3D images displayed to the surgeon. The optical assembly is adjustable to change the view and the visual images are overlaid by the MR images. The visual image can be adjusted in response to movement of the surgical tool and the MR image displayed and/or the image obtained can be modified in response to change in the visual image and/or movement of the tool. The components in the bore are made compatible with the MR environment.