Objective: To evaluate persistence among glaucoma patients with prostaglandin therapy during the first therapy year. Methods: Patients with latanoprost (LAT), bimatoprost (BIM), or travoprost (TRAV) dispensed during January 1, 2004-December 31, 2004 were screened for inclusion (Ingenix managed care database). Index agent=first agent filled; index date=fill date; follow-up=358 days. Patients excluded if: age <40 years; not continuously enrolled for 180 days before/358 days after index date; had ocular hypotensive dispensed or had no glaucoma diagnosis within 180 days before index date. First year persistence measures: whether last fill had sufficient days supply to achieve medication possession at year's end; number of days for which index agent was available (days covered). Possible inconsistencies between quantity dispensed and reported days supply addressed by multiplying claimed days supply with alternative measures from the literature. Models of associations between index agent and medication possession (logistic regression) and days covered (linear regression) were adjusted for gender, age, and previous ocular hypertension diagnosis. Results: A total of 7783 patients met inclusion criteria (LAT, n=4994; BIM, n=1464; TRAV, n=1415). Overall medication possession was 28% and number of days covered was 131 using unadjusted days supply estimate. Compared to LAT, odds of achieving medication possession at year's end were 26%-34% lower for BIM and 34%-36% lower for TRAV (p=0.001 for all comparisons for each imputation). Days covered were 21-29 days lower for BIM and 33-42 days lower for TRAV (p=0.001 for all comparisons). Failure to refill a 2.5 mL size bottle within the first 90 days had 90%-99% specificity for predicting <75% days covered. Conclusion: Persistence with ocular prostaglandins remains a concern. LAT users were more likely to achieve medication possession and had more days covered during the first therapy year than those treated with BIM or TRAV. Failure to refill the index agent within the initial 90 days predicted poor persistence.