In order to determine the horizontal effects of bilateral superior oblique tenotomy, all cases of superior oblique tenotomy performed at the Children's Hospital Medical Center and also in a private practice setting over the past ten years were analyzed retrospectively. A total of 18 patients underwent isolated bilateral oblique tenotomy. An average primary position exo-shift of 2 prism diopters was found; in upgaze a significant exo-shift of 11 prism diopters and in downgaze a significant eso-shift of 21 prism diopters were noted. Analysis of data in the literature on the effects of superior oblique tenotomy suggests that the results of others have, in fact, been consistent with our findings, despite the common misconception that an eso-shift in the primary position was to be expected.