PURPOSE: To evaluate whether data on length of time from patient referral to treatment completion, collected routinely as part of a quality improvement program, can be used to measure the effectiveness of a patient navigator program. PATIENTS AND METHODS: During a calendar year, 72 disparities patients, 38 of whom received navigator services, and a group of 157 nondisparate, un-navigated patients received external beam radiation therapy at a community center. Data from referral time through completion of treatment, which had been collected routinely under an existing continuous quality improvement program, were compared retrospectively, as well as missed treatments and the percentage of planned treatments completed, for three patient groups. RESULTS: The average number of days from referral to consult and from consult to start of treatment were lower for the navigated disparate group (6.66 and 14.56 days, respectively) than un-navigated groups (disparate: 7.37 and 15.97 days; non-disparate: 8.97 and 16.24 days, respectively). The percentage of patients completing treatment was lower for the navigated group (85%) than the un-navigated groups (95% and 97%), despite equivalent treatment percentage completion rates for all groups (97.0% to 98.8%). The navigated group missed more treatment days (1.86 days/patient) than the un-navigated disparate group (0.47 days/patient) or the non-disparate group (0.83 days/patient.) CONCLUSION: Some statistically insignificant differences were noted in favor of patient navigation (PN) but the significance is unclear because of the large data spread and the small numbers of patients. Given that the study was retrospective, it is also unclear whether these differences were influenced by the patient navigator. Repeat studies using the same data elements will provide a better platform for assessing whether such data can provide a measure of the effectiveness of PN in the radiation oncology setting. Given that the patients were not observed routinely by the navigator after the start of treatment unless a particular barrier was identified, there is an opportunity to assess whether interventions by the navigator could improve treatment completion rates and reduce the number of missed treatments.