Among 78 children who had undergone surgery for intermittent exotropia, undercorrection was found in 39, an acceptable result in 33 and overcorrection in 6. A review conducted to determine what factors might explain the high frequency of undercorrection showed that the average age of the patients was higher than usual, and this was a significant prognostic factor. The presence or absence of associated hypertropias, lateral incomitance and A or V patterns was not of prognostic importance. Purposeful overcorrection of the exodeviation by 10 to 15 prism diopters tended to ensure a more satisfactory result.