PURPOSE: To describe a phenomenon, depression in attempted abduction, not previously recognized as a feature of Duane syndrome (DS). DESIGN: Retrospective, observational case series. METHODS: Setting: Institutional practice. PATIENT POPULATION: Patients diagnosed with esotropic DS at Boston Children's Hospital from 2002 to 2015. Patients with clinical photographs documenting horizontal gaze were included. Patients with prior strabismus surgery were excluded. OBSERVATION PROCEDURES: Patients were classified into 3 groups according to their vertical eye position in attempted abduction: midline group, depression group, and elevation group. Group assignment was performed by 3 independent ophthalmologists. Baseline characteristics, eye movement, and ocular deviation were compared among the 3 groups. MAIN OUTCOME MEASURES: Horizontal and vertical deviation on attempted abduction in the DS eye. RESULTS: Depression in attempted abduction was present in 74 of 113 unilateral patients (66%) and 18 of 42 gradable eyes (43%) of bilateral patients. Abduction limitation was significantly less severe in the midline group (median: -3.0) than in the depression group (median: -4.0) (P = .01). Vertical deviation in attempted abduction was more severe in the elevation group than in the depression group (P = .003). CONCLUSIONS: Depression of the eye in attempted abduction has not been widely described, yet it is present in the majority of DS patients. It is more likely to occur with more severe abduction limitation. This phenomenon is likely another form of dysinnervation in DS, the result either of anomalous vertical rectus muscle activation or asymmetric lateral rectus muscle innervation during attempted abduction. Awareness of vertical deviation in attempted abduction may facilitate surgical planning in affected patients.