Objective: To evaluate healthcare resource utilization (HRU) by patients treated with onabotulinumtoxinA for chronic migraine (CM) in a subanalysis of the COMPEL study. Background: Population-based studies have shown that patients with CM have greater headache-related disability, increased HRU, and higher direct and indirect costs. Design/Methods: The single-arm, open-label COMPEL study (NCT01516892) enrolled adults with CM receiving onabotulinumtoxinA 155 U approximately every 12 weeks (9 treatments). Patients recorded headache (HA) days in a daily diary to assess mean change from baseline in the number of HA days/28-day period up to 108 weeks. HRU data, including total HA-related visits to a healthcare professional (HCP), emergency room (ER)/urgent care (UC) visits, overnight stays, and number of HA-related diagnostic tests, were collected at baseline and at each treatment session. P-values were based on t-test or Wilcoxon signed rank test. Results: Patients (N=716 enrolled) were, on average, aged 43 years, female (85%), with a family history of migraine (63%). At baseline, 557 patients reported a mean (SD) of 7.0 (15.4) and a minimum-maximum of 0–198 HA-related visits to an HCP. Visit frequency was significantly reduced at all time points. The majority of patients reported seeing a neurologist/HA specialist, followed by a primary care physician. At baseline, 690 patients reported a mean (SD) of 0.5 (2.0) HA-related ER/UC visits, and 691 patients reported 0.2 (1.5) HA-related overnight hospital stays. Following onabotulinumtoxinA treatment, HA-related ER/UC visits and overnight hospital stays were significantly reduced at all time points. At baseline, 193 patients reported a total of 487 HA-related diagnostic tests. A total of 334 HA-related diagnostic tests were reported from weeks 24 to 96. Commonly reported diagnostic tests at baseline included blood tests (21.0%), MRI (18.7%), and CAT/CT scans (10.9%). Conclusions: Real-world findings from the COMPEL study show that onabotulinumtoxinA treatment is associated with HRU reductions. Disclosure: Dr. Rothrock has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Allergan, Amgen, Lilly, and Supernus. Dr. Rothrock has received research support from Allergan plc, Amgen, and Dr. Reddy’s Laboratories. Dr. Stark has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Has received advisory board and/or lecture fees from Allergan, Biogen, Eli Lilly, Novartis, SciGen, and Teva.. Dr. Stark has received personal compensation in an editorial capacity for Has received advisory board and/or lecture fees from Allergan, Biogen, Eli Lilly, Novartis, SciGen, and Teva.. Dr. Sommer has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Employee of Allergan. Dr. Sommer holds stock and/or stock options in Katherine Sommer, MRes, PhD, is an employee of Allergan plc and receives stock or stock options. which sponsored research in which Dr. Sommer was involved as an investigator. Dr. Sommer holds stock and/or stock options in Employee of Allergan and receives stock options. Dr. Blumenfeld has received personal compensation for consulting, serving on a scientific advisory board, speaking, or other activities with Received compensation for consulting and promotional activities from: Allergan, Alder, Amgen, Teva, Lilly, Biohaven, Theranica, Supernus, Novartis.. Dr. Blumenfeld holds stock and/or stock options in Alder, sold. Dr. Blumenfeld has received research support from Not personally, many research projects funded by Pharma were done with The Neurology Center, who also employs me..