The right and left mammograms of a patient are assumed to be bilaterally symmetric for image readings. The detection of asymmetry in bilateral mammograms is a reliable indicator for detecting possible breast abnormalities. The purpose of this study was to examine the potential usefulness of a new method in terms of spatial frequency components for exploration of similarity and abnormality between the right and left mammograms. A total of 98 normal and 119 abnormal cases with calcifications were used for this study. Each case included two mediolateral oblique views. The spatial frequency components were determined from the symmetric regions in the right and left mammograms by Fourier transform. The degrees of conformity between the two spatial frequency components in the right and left mammograms were calculated for the same and different patients. The degrees of conformity were also examined for cases with and without calcifications for the same patient to show if the proposed method was useful for indicating the existence of calcifications or not. The average degrees of conformity and the standard deviations for the same and different patients were 0.911 ± 0.0165 and 0.857 ± 0.0328, respectively. The degrees of conformity calculated from abnormal cases (0.836 ± 0.0906) showed statistically lower values compared with those measured from normal cases (0.911 ± 0.0165). Our results indicated that histogram analysis of spatial frequency components could be useful as a similarity measure between bilateral mammograms for the same patient and abnormal signs in a mammogram.