This study was an observational, open-label, cohort-study conducted in accordance with the principles of the Helsinki Declaration. We prospectively and systematically recorded data from the patients and analyzed them retrospectively. During a first phase, called adaptation period, the injector (DR) used a follow-the-pain approach in order to determine the optimal injection scheme for each individual. The possible injection sites were the corrugator, temporalis, and trapezius muscles. Patients were systematically asked about the usual topography and time course of migraine attacks, and the existence of pain or stiffness of the cervical muscles. If the pain was predominantly located in the frontotemporal area, the corrugator and temporalis muscles were injected bilaterally. When the patients had predominant pain in the back of the head, or when their headache pain frequently started and/or ended in the trapezius muscles, both trapezius muscles were injected. These muscle groups were injected together if pain was both frontotemporal and cervico-occipital. When this first set of injections was efficacious, patients were re-injected in the same manner at the time when the frequency of headache days definitely increased. In the absence of efficacy, the paradigm was modified using the same follow-the-pain approach. Once the best procedure was determined for each patient, it was reproduced at each subsequent injection session. This adaptation phase could necessitate up to three sessions. The observation period started 8 weeks before the first efficacious injection and ended 2 months after the second consecutive efficacious injection, or in case of inefficacy. Throughout the adaptation and the observation phases, patients kept a headache diary where they were asked to note the days with headache and the use of rescue medication.