PURPOSE. The purpose of this study was to compare the new, computerized Aniseikonia Inspector with the Space Eikonometer for the measurement of aniseikonia. METHODS. Eighteen subjects, ages 21 to 61 years, with normal binocular vision and normal visual acuity had aniseikonia measured with both the Aniseikonia Inspector Version I and the Space Eikonometer. Aniseikonia was measured first with the subjects' habitual refractive correction and then with afocal size lenses of 1%, 2%, and 3.5% added in random order before the right and left eyes. Measurements were taken initially with the Aniseikonia Inspector and on a subsequent day with the Space Eikonometer. RESULTS. For the Space Eikonometer, the slopes of the lines for the relationship between the measured aniseikonia and the induced magnification differences in the vertical and horizontal meridians are not significantly different from 1.0. For the Aniseikonia Inspector, the slopes of the lines in the vertical and the horizontal meridians are less than and significantly different from 1.0. On average, the Aniseikonia Inspector underestimates the magnitude of induced aniseikonia, predicting only 68% and 61% of the overall size lens magnification in the vertical and horizontal meridians, respectively. The corresponding values of the Space Eikonometer in the vertical and horizontal meridians are 99% and 93%. Variability is greater with the Space Eikonometer than the Aniseikonia Inspector. CONCLUSION. The Space Eikonometer appears to be measuring the induced aniseikonia appropriately, whereas the Aniseikonia Inspector underestimates the amount of aniseikonia. However, the Space Eikonometer shows greater measurement variability. Modification of the Aniseikonia Inspector or the testing conditions should be pursued in future studies. © 2006 American Academy of Optometry.