BACKGROUND: The present study aimed to evaluate the risk and impact of fibromyalgia in relation to headache frequency in migraine patients. METHODS: This cross-sectional study involved migraine patients from a regional hospital and a tertiary medical center. Diagnoses of migraine and fibromyalgia were made according to the International Classification of Headache Disorders, 3rd edition, and the modified 2016 American College of Rheumatology diagnostic criteria, respectively. Clinical data, including Fibromyalgia Symptoms (FS) scale and revised Fibromyalgia Impact Questionnaire (FIQR), were collected systematically by questionnaires-based interviews. Patients were categorized based on monthly headache day (MHD) cut-offs derived from decision tree analysis based on the chi-squared automatic interaction detection algorithm. RESULTS: The study involved 2082 migraine patients (1619 female/463 male, mean ± SD age 39.3 ± 12.0 years), including 132 with fibromyalgia (118 female/14 male, mean ± SD age 44.1 ± 12.7 years) (6.3%). Patients were divided into three groups: ≤9 MHDs (n = 924), 10-20 MHDs (n = 745) and ≥21 MHDs (n = 413). The percentage of fibromyalgia increased with headache frequency ( CONCLUSIONS: There was an independent dose-response association between headache frequency and odds, severity, and impact of fibromyalgia in migraine patients. For migraine patients with a higher headache frequency, the potential risk of comorbid fibromyalgia should not be overlooked given its association with more severe clinical manifestations and greater disability.