A simple method has been used to boresight an IR imager. The mechanical axis is defined by a plane parallel mirror attached to a reference mechanical flange. The difference between the optical and mechanical axis was measured by a dual-band modified autocollimator. The boresight is achieved by a vertical lateral movement of the lens relative to the detector for vertical orientation and by a zero offset of the scanning mirror direction for horizontal orientation. The accuracy of the measured angles depends on the focal length of the autocollimator optics and the electronics for measuring the image position by the video output of the thermal imager.