Standard (qualitative) electroencephalography (EEG) is routinely used in the diagnostic evaluation of psychiatric patients. Quantitative EEG (qEEG) findings differ between patients with schizophrenia, patients with depression, but results are not consistent. The aim of our study was to determine the differences in qEEG parameters between patients with schizophrenia, patients with depression, and healthy subjects.The study included 30 patients with schizophrenia, 33 patients with depression, and 30 healthy subjects. All study participants underwent standard EEG. Artifact-free 100-second epochs were selected from the recorded material and analyzed with Fast Fourier Transformation (FFT) analysis.The results are presented as absolute spectral power values (μV2) of delta, theta, alpha, and beta components of the EEG spectrum. EEGs were recorded from 12 locations including Fp1, Fp2, F3, F4, F7, F8, T3, T4, P3, P4, O1, and O2. In comparison with healthy subjects, patients with schizophrenia showed increased delta, theta, and beta activity and decreased alpha activity. Similar results were obtained in patients with depression, but in fewer regions. In patients with schizophrenia, delta power over Fp1, Fp2, F4, and F8 regions was increased in comparison with those in patients with depression. Interhemispheric asymmetry was found in patients with schizophrenia and healthy subjects, but not in patients with depression.The finding that patients with schizophrenia differed from patients with depression in delta power values could be potentially used in differential diagnosis between schizophrenia and depression. The role of qEEG in clinical differentiation between these two mental disorders may be especially important in cases of negative-symptom schizophrenia.