Absence seizures evolving to bilateral tonic-clonic seizures may have focal or asymmetric clinical features. Using quantitative electroencephalography (EEG) may evaluate this phenomenon and the involved neuronal network. We conducted a retrospective chart review of pediatric patients with generalized epilepsy and normal brain magnetic resonance imaging (MRI) admitted to an epilepsy monitoring unit. Our results show that seven of 66 patients with generalized epilepsy, all females, had generalized onset seizures with focal evolution (GOFE) to bilateral tonic-clonic seizures. Age at seizure onset was 7.5 years, at epilepsy syndrome diagnosis 8.14 years, and at GOFE diagnosis 13.04 years. Three had juvenile absence epilepsy, two had juvenile myoclonic epilepsy, and two had generalized genetic epilepsy. Eight seizures were recorded. Six patients had normal EEG background and one mild slowing. Quantitative EEG (QEEG) spectrogram with spike detection analysis showed 2.5-3.5-Hz generalized spike-wave activity followed by focal buildup over the lateral frontal, occipital, and frontal-central regions (right more than left) before bilateral tonic-clonic progression. In conclusion, in our cohort of patients with GOFE, QEEG analysis accurately showed that after absence seizure there is focal activation of the frontal (mainly right) and occipital cortices with evolution to bilateral tonic-clonic seizure. We hypothesize that GOFE could involve the activation of the thalamus and the cortex via the thalamocortical network, based on the QEEG analysis and the literature functional MRI evidence in absence seizures. Additional study of more patients to confirm findings is required.