The precise slice geometry of a CT scanner is an important, albeit tedious to determine, characteristic. A series of computer programs have been developed to analyze the slice thickness insert of the AAPM phantom. Without operator assistance they generate the beam profiles and slice thicknesses at three points in the scan field. A representative analysis is done on an AS&E scanner with slice thickness settings of 2 to 10 mm. The resulting discrepent measured thicknesses, ranging from 3 to 8 mm, indicate the need to perform such slice thickness measurements as part of a regular quality assurance program.