In patients with a first seizure, the identification of early sensitive and specific biomarkers for formulating a diagnosis of epilepsy is fundamental. Sleep deprivation (SD) has long been used as a means of enhancing EEG sensitivity in the diagnostic process. However, huge methodological differences among the studies addressing this topic have led to highly variable results and often confusing assumptions. Here, we provide a detailed description of the correlations between SD and epilepsy, along with their putative mechanistic explanations derived from experimental studies in animals and humans. We also outline the clinical studies evaluating the role of SD EEG and discuss them critically in terms of: (a) study design and SD EEG methodology; (b) EEG sensitivity and specificity; (c) the role of drug-induced sleep EEG and EEG during spontaneously occurring sleep; and (d) the relevance of patient features, syndromes, and subsyndromes, as well as their correlations with neuroimaging details. Finally, we propose specific studies that might increase the role of SD EEG in the diagnosis and prognosis of epilepsy.