AIM: To study the factors affecting residual exotropia (>10 PD) at 4-6wk postoperative visit following two rectus muscle surgery for intermittent exotropia [bilateral lateral rectus (LR) recession or unilateral recess resect procedure]. METHODS: A retrospective chart review of patients with intermittent exotropia ≤50 PD who underwent two rectus muscle surgery in between Jan. 2011 to Dec. 2013 was performed. Possible factors were compared between patients with residual exotropia (>10 PD) and successful outcome (within 10 PD of orthotropia) at the 4-6wk postoperative visit. Effect/dose ratio was calculated by dividing the effect of surgery by the total amount (mm) of muscle surgery done. RESULTS: One hundred and fifty-seven patients with mean age of 14y (range 3-53y) were included. Twenty-seven patients (17.2%) had residual exotropia at 4-6wk postoperative follow up. Age at surgery (P=0.009) and preoperative deviation for distance (P≤0.001) and near (P=0.001) were identified as important predictors of unsuccessful outcome. The occurrence of residual exotropia was not affected by amblyopia, anisometropia, lateral incomitance, pattern deviation, vertical deviation, type of exotropia or type of surgery done (recess-resect or bilateral LR recession). The effect/dose ratio was more in deviations >40 PD in the both recess-resect and bilateral LR recession type of surgery. The effect/dose ratio was less in patients with residual exotropia as compared to the successful outcome group (1.36 PD/mm vs 2.05 PD/mm in the bilateral LR recession surgery and 1.93 PD/mm vs 2.63 PD/mm in the unilateral recess-resect surgery). CONCLUSION: Residual exotropia is seen in 17% of patients after two muscle surgery for intermittent exotropia. Patients with older age and larger preoperative deviation have greater chances of developing failure of two muscle strabismus surgery for intermittent exotropia.