The data for 94 consecutive patients with intermittent exotropia of basic type, ranging from 20 to 40 prism diopters (delta), who preoperatively wore neutralizing prisms for 3 to 5 days, were studied retrospectively. The surgery in 43 patients in whom the amount of increase of angle was 4delta or less was based on the original angle (Group A), while that in 51 patients in whom the magnitude of increase was 5delta or more was based on the increased angle of deviation (Group B). Patients with initial deviation less than 30delta and patients younger than 7 years of age showed an increase of deviation with prism correction. There were no significant differences in surgical results between the two groups at 1 year, and at 3 years; although at 3 years satisfactory motor alignment and binocular function for single vision at distance was higher in Group B than that in Group A.