Epilepsy and headache are the two most common neurologic disorders affecting individuals of all ages worldwide. They constitute an important health and socioeconomic problem 1,2 . Approximately 50 million people suffer from epilepsy 3 , while in the adult population the prevalence of active headache is around 46% 2 . Drug treatment of epilepsy, with antiepileptic drugs, and headache, with prophylactic drugs, is prolonged in most cases (years to decades). Moreover, although for both pathologies it is recommended the use of a single antiepileptic or prophylactic drug, the use of polytherapy is very common [4][5][6] . Therefore, there is high risk of interactions between the drugs used for the primary neurologic disorder and other ones necessary throughout life for different acute or chronic conditions.In the treatment of chronic diseases, such as epilepsy and migraines, it is important to know the side effects of the prescribed drugs, as well as their contraindications and interactions, since most patients will need at some point to use medications for other associated diseases [4][5][6][7] . Once they are diseases that affect individuals at any age, chronically, comorbidities are common in people with epilepsy and headache and they lead to the use of other medications, which are added to the primary neurological drugs. In subjects with migraine, the second most common type of chronic headache, a long list of comorbidities are reported, AbsTRACT Comorbidities are often associated with chronic neurological diseases, such as headache and epilepsy. Objectives: To identify comorbidities associated with epilepsy and headaches, and to determine possible drug interactions. Methods: A standardized questionnaire with information about type of epilepsy/headache, medical history, and medication was administered to 80 adult subjects (40 with epilepsy and 40 with chronic headache). Results: Patients with epilepsy had an average of two comorbidities and those with headache of three. For both groups, hypertension was the most prevalent. On average, patients with epilepsy were taking two antiepileptic medications and those with headache were taking only one prophylactic medication. Regarding concomitant medications, patients with epilepsy were in use, on average, of one drug and patients with headache of two. Conclusions: Patients with chronic neurological diseases, such as epilepsy and headaches, have a high number of comorbidities and they use many medications. This may contribute to poor adherence and interactions between different medications.Key words: epilepsy, headache, drugs interaction. REsumoAs comorbidades geralmente estão associadas a doenças neurológicas crônicas, tais como cefaleia e epilepsia. Objetivos: Identificar comorbidades associadas à epilepsia e cefaleia e determinar as possíveis interações de drogas. Métodos: Questionário padronizado com informações sobre o tipo de epilepsia/cefaleia, os antecedentes médicos e as medicações foi aplicado a 80 indivíduos adultos (40 com epilepsia e 40 com cefaleia crônica). ...