We conducted a retrospective study of 133 children (69 boys and 64 girls) who underwent bilateral medial rectus muscle recession (most by the augmented or en-bloc technique) for congenital esotropia. Esotropia was diagnosed before the age of 6 months in 84 patients and after the age of 6 months in the other 49. A total of 27 children underwent surgery before the age of 12 months; of these, three required second procedures. A total of 106 children underwent surgery after the age of 12 months; of these, eight required second procedures. The mean preoperative deviation was 40 prism diopters. Two patients had significant A pattern deviations and 17 had significant V pattern deviations. Six patients had dissociated vertical deviations. Five to 60 days after surgery, 52 patients had no deviation and 99 were within +/- 10 prism diopters of no deviation. Two months after surgery, 67 patients had no deviation and 114 were within +/- 10 prism diopters of no deviation. Final alignments (five months to seven years postoperatively) showed that 51 patients had no deviation and 109 were within +/- 10 prism diopters of no deviation. Despite adequate alignment, none of 13 patients whose esotropia was diagnosed before the age of 6 months, who underwent surgery before the age of 12 months, and who cooperated with testing achieved stereopsis. This suggested that there may be two types of congenital esotropia--one without fusion potential and one in which fusion is possible but lost secondarily because of peripheral esotropic factors.