Display omitted •Different generalized tonic clonic seizure (GTCS) subtypes occur in various genetic generalized epilepsy syndromes and in individual patients.•At onset, GTCS subtypes activate similar brain regions but differ in long-range connectivity.•GTCS evolution to tonic-start epoch associates with reduced long-range connectivity, particularly at δ/θ frequencies. To determine EEG spatiospectral activation and connectivity in the generalized tonic-clonic seizure (GTCS) semiological subtypes. 39 patients with genetic generalized epilepsy (GGE) who had GTCS (n = 58) during video-EEG monitoring were identified in the Vanderbilt Epilepsy database. GTCSs were classified as absence tonic-clonic, myoclonic tonic-clonic, or tonic-clonic. Patient characteristics and semiological features were compared. Spectral power and node degree, a network measure of connectivity, were calculated at two seizure epochs, electrographic and tonic-start. Different GTCS subtypes occurred within individual patients. At electrographic-onset, all subtypes activated midline frontal cortex at delta/theta and beta frequencies but differed in network connectivity. In all subtypes, GTCS evolution from electrographic to tonic-start associated with preserved beta frequency spectral power, but reduced connectivity and delta/theta power. Our findings suggest that at GTCS onset, the subtypes activate similar cortical regions and their different initial semiologies relate to their distinct onset long-range connectivity. Upon transition to the tonic-start epoch, the ictal activity is predominantly conveyed by β frequency activity and connectivity. Future neurostimulation therapies for medically intractable GTCSs may target the same brain regions for all GTCS subtypes and may be most effective prior to the tonic-start epoch.