OBJECTIVES: To determine the value of a web portal by quantifying the differences in medication adherence between web-users and non-web-users. METHODS: A case-control study design was employed for this study. Prescription records from a de-identified pharmacy claims database maintained by a large pharmacy benefit manager were obtained between April 1st 2009 to March 31st 2010. The test group consisted of patients who filled their prescriptions via a web-based portal. Patients who were enrolled in similar health plans but never used the web portal to fill their prescriptions comprised the control group. All eligible patients included in this analysis were continuously enrolled during the study period. Differences in medication possession ratio (MPR), defined as the sum of days that patient possessed any maintenance medication divided by the total number of days in the follow-up period, was calculated during the observation period and compared using a paired t-test. Additionally, MPRs for the Top 10 therapeutic medication classes were computed and compared across test and control group. RESULTS: A total of 2,333,635 eligible patients were included in the study. Among them 53,018 patients met the criteria for test group and 2,280,617 patients were included in the control group. Overall mean MPR for the test group was found to be significantly higher (0.48 Vs 0.37) as compared to the control group (p<0.05). Additionally, across all the Top 10 medication classes, the test group patients’mean MPR was significantly higher than that of  control group patients. CONCLUSIONS: Patients, who filled their prescriptions via the web portal, have higher adherence rates as compared to those who do not choose this channel to fill their scripts. Further studies aimed at evaluating key drivers for the differential adherence rate are required to gain additional insights about the importance of web-portal as a tool for refilling prescriptions.