OBJECTIVE To study the frequency and characteristics of slipped extraocular muscles after strabismus surgery and report the postoperative outcomes longitudinally. METHODS Retrospective chart review. METHODS Electronic medical records of 493 patients who underwent strabismus surgery and were found to have a slipped muscle intraoperatively were reviewed. METHODS Records were retrieved and operative reports were screened for the presence of slipped muscles. Data pertaining to the eye examination and surgery were collected, including vision, ocular motility in all positions, duction limitations, slipped muscle, empty sheath length, amount of slippage, amount of advancement, and amount of recession of the antagonist muscle. RESULTS Twelve patients (mean age 29.1 ± 6.4 years; 5 males) were found to have 15 slipped medial rectus muscles. Average amount of slippage was 15.7 ± 2.0 mm; from limbus empty sheath length was 5.9 ± 1.9 mm. Average preoperative deviation was 32.2 ± 10.0 prism diopters (PD) exotropia. Mean follow-up after corrective surgery was 13.3 months (1 week to 42 months). Four patients were transiently overcorrected postoperatively (7.0 ± 7.0 PD esotropia). The rest had mean residual exotropia of 13.5 ± 9.2 PD with a change of 26.6 ± 10.3 PD from baseline (p < 0.001). Intraoperative mean muscle movement was 10.3 ± 2.2 mm with a mean postoperative change of 2.6 PD for each 1 mm of muscle advancement. There was no significant increase over time in the postoperative angle of deviation during all follow-up periods except for 1 patient who was re-explored after 4 years. CONCLUSIONS Slipped muscle should be suspected in the presence of limited ductions and consecutive deviations after strabismus surgery. A change of 2.6 PD for every 1 mm of medial rectus muscle advancement was observed and maintained over time.