Glaucoma medications can reduce intraocular pressure and improve clinical outcomes when patients adhere to their medication regimen. Providers often ask glaucoma patients to self-report their adherence, but the accuracy of this self-report method has received little scientific attention. Our purpose was to compare a self-report medication adherence measure with adherence data collected from Medication Event Monitoring Systems (MEMS) electronic monitors. Additionally, we sought to identify which patient characteristics were associated with over-reporting adherence on the self-reported measure