OBJECTIVE: To evaluate eye drop administration by patients at multiple visits in the setting of a randomized controlled trial. STUDY DESIGN AND METHODS: Patients with glaucoma or ocular hypertension were randomized to 12 weeks of treatment with topical ocular hypotensive medication in a multicenter, investigator-masked trial. At baseline, patients were given a questionnaire for self-assessment of difficulty with drop administration. At baseline and 12 weeks, patients demonstrated drop instillation using a bottle of artificial tears. MAIN OUTCOME MEASURES: Patient self-assessment of difficulty with drop administration and observed patient difficulty with drop administration, defined as bottle touching eye/adnexa, drop missing the ocular surface, or administering more than 1 drop. RESULTS: Of 164 enrolled patients, 50% had previously been treated with ocular hypotensive medication for ≥3 years. Only 11.4% of patients reported difficulty with eye drop administration at study entry. At baseline, 18.2% of patients touched their eye/adnexa with the bottle and 10.3% missed the eye. At 12 weeks, 18.5% and 8.6% of patients, respectively, had similar difficulties. Overall, difficulty with drop instillation was observed in 42.1% of patients. Difficulty at both visits was seen in 35.3% of patients who reported difficulty at entry and in 17.2% of patients who denied difficulty. The relative risk of demonstrating difficulty at either visit was 2.0 times greater for patients who self-reported difficulty at study entry (P = 0.004). The relative risk of demonstrating difficulty at week 12 was 3.8 times greater for patients with observed difficulty at baseline (P < 0.001). Limitations of the study design included self-administration of drops to the eye of the patient's choice and observation in an office setting. CONCLUSIONS: Patients with experience instilling topical glaucoma medications continue to have difficulties with eye drop administration, including patients who do not self-report difficulty. The risk of difficulty with eye drop administration is increased in patients who self-report difficulty and in patients who have been previously observed to have difficulty. CLINICAL TRIAL REGISTRY NUMBER: NCT01253902.