A single-mode silver halide symmetric step-index planar waveguide for 10.6 microm is described. We fabricate the waveguide from extruded multimode silver halide fiber by pressing the fiber between metal plates while heating. The device is therefore automatically pigtailed to a fiber, which could ease the difficulties of coupling light into it. We achieved single-mode confinement by suitably adjusting the refractive index of the core and the cladding and by reducing the core thickness to 30 microm. The output radiation from the planar waveguide was measured to confirm single-mode confinement. Silver halide single-mode waveguides for the mid-infrared can be used to enhance sensitivity in fiber-optic evanescent-wave infrared spectroscopy measurements or for the development of mid-infrared single-mode lasers and interferometers.