Objective To examine treatment utilization patterns and safety of onabotulinumtoxinA for the prophylactic treatment of chronic migraine in routine clinical practice. Background Clinical trials support onabotulinumtoxinA for the prophylaxis of headache in patients with chronic migraine, but real-world data are limited. Design/methods A prospective, observational, post-authorization study in adult patients with chronic migraine treated with onabotulinumtoxinA. Data were collected at the first study injection and approximately every three months for ≤52 weeks for utilization and ≤64 weeks for safety data, and summarized using descriptive statistics. Results Eighty-five physicians (81% neurologists) at 58 practices in the United Kingdom, Germany, Spain, and Sweden participated and recruited 1160 patients (84.2% female, median age 46.6 years). At baseline, 85.8% of patients had physician diagnoses of chronic migraine/transformed migraine and reported an average of 11.3 (SD = 6.9) severe headache days per 28 days; 50.6% had previously used onabotulinumtoxinA for chronic migraine. A total of 4017 study treatments were observed. The median number of injection sites (n = 31) and total dose (155 U) were consistent across all treatment sessions, with a median 13.7 weeks observed between sessions. At least one treatment-related adverse event was reported by 291 patients (25.1%); the most frequently reported treatment-related adverse event was neck pain (4.4%). Most patients (74.4%) were satisfied/extremely satisfied with onabotulinumtoxinA treatment. Conclusions Patient demographics/characteristics are consistent with published data on the chronic migraine population. Utilization of onabotulinumtoxinA treatment for chronic migraine appears to be consistent with the Summary of Product Characteristics and published PREEMPT injection paradigm. No new safety signals were identified.