The usefulness of conventional EEG in primary psychiatric disorders is under debate. Most recordings in these patients offer nonspecific findings or physiological characteristics. The use of qEEG in early stages has not yielded consistent results. However, in recent years, the use of this tool has been reconsidered, albeit from a scientific and research perspective. This approach aims to obtain consistent results that, in a second phase, can be extrapolated to clinical practice. Changes in spectral composition, especially increased delta and theta power, decreased and redistributed alpha rhythms, and modifications in the synchronization structure have provided promising data for improved clinical diagnosis of these pathologies.