OBJECTIVE: To assess glaucoma medication adherence in children, hypothesizing that poor parental health literacy and eye drop instillation by the child are associated with worse adherence. METHODS: This prospective, observational study enrolled pediatric patients with glaucoma who were prescribed eye drops. Parent(s) reported who was responsible for eye drop instillation (parent vs child), took the Rapid Estimate of Adult Literacy in Medicine, and were instructed on the use and purpose of the Medication Event Monitoring System. Calculations included average adherence (proportion of prescribed doses taken), dosing errors (number of overdosing or underdosing events in 24 hours), and proportion of doses taken on schedule (doses taken within 2 hours of prescribed dosing interval). Results are reported as mean (SD) or median. RESULTS: The study included 46 of the 50 enrolled children who used the Medication Event Monitoring System for 30 days or more. Adherence ranged from 43% to 107% (93% [12%]) and was not associated with age (slope, 0.09 [0.52]; P = .86) but decreased with the parent's lower health literacy (slope, 0.62 [0.24]; P = .01).The mean number of dosing errors for medications prescribed daily vs twice daily was similar (3.3 vs 2.9; P = .66). The proportion of doses taken on schedule (within 2 hours of prescribed dosing interval) ranged from 3% to 97% (median, 34%; mean, 41% [24%]) and was better when the parent vs the child instilled eye drops (46% [26%] vs 23% [19%]; P < .001). CONCLUSIONS: Time-dependent glaucoma medication adherence was better when the parent was responsible for eye drop instillation. Overall decreased adherence was associated with decreased parental health literacy. Children of parents with poor health literacy are vulnerable to poor medication adherence; efforts to address poor health literacy may improve outcomes.