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The objective of this study is to investigate ictal and interictal cortical involvement in epilepsy associated with hypothalamic hamartoma. We conducted a retrospective study of 34 patients with epilepsy and hypothalamic hamartoma, using data from long-term video-EEG-monitoring. We analyzed onset and propagation of ictal and interictal scalp EEG and visualized the resulting networks of cortical involvement. According to clinical and EEG criteria we grouped patients in: 1) focal disease, 2) focal advanced disease, 3) extended disease. We compared networks between these groups and different seizure types. Eight patients underwent several video-EEGs, and we analyzed all to investigate epilepsy progression. Epileptic activity mainly involved frontal and temporal cortex regions. Involvement of frontal regions was more common in advanced stages of the disease, and strong fronto-temporal connections were observed in the ictal networks of patients in intermediate stages [25.0% (left) and 35.7% (right) of seizures with EEG correlate]. The occurrence and timing of EEG-correlate significantly depended on the seizure type (χ2-test, P ≪ 0.001). In patients with several EEGs, seizure activity increased by +0.67 seizures/day/month (mean). There were significant differences between patients with normal and impaired cognitive function, with the latter showing pronounced ictal involvement of fronto-temporal cortex areas (P < 0.001). Overall, in epilepsy due to hypothalamic hamartoma, cortical involvement focuses on frontal and temporal regions and varies systematically with the stage of the disease, different seizure types, and the presence of impaired cognitive function. We propose that these data may help improve our general understanding of epileptogenesis and potentially provide insights for the surgical therapy of hypothalamic hamartomas. NEW & NOTEWORTHY: Data from routine long-term video-EEG (VEEG) monitoring can be used to visualize and analyze networks of cortical involvement in patients with hypothalamic hamartoma. Involvement of temporal cortex areas is frequent even in patients with relatively mild disease and might be an early sign of dissemination. Repeated VEEGs in eight patients show an overall increase in seizure activity and interictal epileptiform discharges (IEDs) and changes in the networks of cortical involvement over time. [ABSTRACT FROM AUTHOR]