Objectives: Patients with chronic migraine (CM) display a considerable amount of comorbidities, particularly psychiatric and cardiovascular, and the presence of multiple comorbidities, that is, the so‐called multimorbidity, is a risk factor for migraine chronification or maintenance of CM. Our aim was to address the rate and impact of multimorbidity in patients with CM and medication overuse headache (MOH). Materials & Methods: In a sample of patients with CM attending a structured withdrawal for coexisting MOH, we defined multimorbidity as the presence of two or more conditions in addition to CM‐MOH. We compared patients with and without multimorbidity for demographic and clinical variables, quality of life, and disability; we also tested whether patients with multimorbidity had higher likelihood to attend emergency room, relapse into CM, and require further withdrawal treatments by 12 months. Results: One hundred and ninety‐four patients were enrolled as follows: 61% had at least one comorbidity, the most common being mental (34%), circulatory (18%), and endocrine conditions (13%); 32% were multimorbidity cases. Patients with multimorbidity had higher headaches frequency, older age, lower education and lower employment rates, higher disability and lower QoL. They were more frequently opioids/barbiturates overusers and were more likely to attend ER (OR: 2.36), relapse into CM (OR: 2.19), and undergo another withdrawal (OR: 2.75) by 12 months after discharge, after controlling for age, gender, years of education, and headache frequency. Conclusions: Recognizing multimorbidity in patients with CM‐MOH is important to enhance the management of these complex patients, who are at risk of polypharmacy and increased health care utilization. [ABSTRACT FROM AUTHOR]