This paper presents the first stereoscopic range measurements at a wavelength of 3.3 mm and discusses the accuracy of this new method. The synthesis of passive millimeter-wave imaging and stereoscopy combines the advantages of both principles, naturally looking high-contrast images and superior poor-weather performance (compared to visible and infrared wavelengths), as well as the passive ranging capability. Our setup using two antennas with a half-power beamwidth (HPBW) of 0.9$^circ$and a stereoscopic baseline of 1.15 m allows ranging with an accuracy of$approxhbox10hbox%$up to a distance of$approx$300 m. The range resolution improves with increasing stereoscopic baseline, lower radiometer noise, narrower antenna beams, and higher scene contrast. For scenes with sufficient contrast, the directional resolution is considerably better than the antenna HPBW. Thus, massive oversampling of the scene in the plane of the stereoscopic baseline is required. For our setup, an oversampling factor of 36 is optimal. Since additional ranging errors result from nonstationary scenes, fast scanning imagers should be applied.