Introduction: Epilepsy affects millions of people and its geographical patterns are usually linked to etiological aspects. Our objective was to describe main etiologies of epilepsy in Mexico.

Patients and methods: We selected patients from the Multicenter Epilepsy Registry carried out from 2021 to 2022 in 89 Mexican hospitals in 31 states, a sample predominantly of pediatric age. Only patients with electroencephalography and neuroimaging studies were included.

Results: We analyzed 6,653 patients with documented etiologies. Etiology frequency with confidence interval (95% CI) was: structural 46.1% (44.9-47.3), genetic 12.9% (12.1-13.7), infectious 2.9%. (2.5-3.3), metabolic 1.4% (1.1-1.7), immune 0.9% (0.8-1.3) and unknown 40.9% (39.8-42.2). The two main structural etiologies were malformations of cortical development and hypoxic-ischemic encephalopathy. Neurocysticercosis represented a minority with only 1%. Structural and genetic etiologies were associated with focal and generalized onset seizures respectively. Status epilepticus was identified, mostly with motor component, associated with immune and infectious etiologies. Comorbidities were found in 61.6%, mainly neurological development disorders. Drug-resistant epilepsy was more common in patients with immune, infectious and structural etiologies.

Conclusions: The main etiology of epilepsy was structural. The frequency of genetic etiology was relatively lower than in other series, possibly due to the limited availability of genetic tests. Despite technological advances, a large fraction of epilepsies still has unknown origin.