Objective: Hyperemesis gravidarum (HG) is a disease characterized by excessive vomiting and nausea during pregnancy. It differs from normal pregnancy where simple nausea and vomiting are seen frequently with unknown cause. The place and role of the brain in HG is unknown. Materials and Methods: Thirty-three healthy pregnant women and 30 patients diagnosed with HG admitted to Selcuk University Faculty of Medicine, Obstetrics and Gynecology Department were included and electroencephalograph (EEG) signals of all patients obtained at Neurology Department were examined. These signals were evaluated with high math and examined with developed engineering methods. The sampling frequency of the EEG was 200 Hz. Data were obtained in the frequency-power axis using 0.1 Hz frequency resolution, Hamming windowing, and 0.5 overlap ratio with signals on the time axis on all channels. All sub-bands have formed with unearthed power spectral density as delta, theta, alpha, and beta and after being created was calculated spectral densities. Results: As a result, while showing significant changes as delta band for Fp1F3, theta band for C3P3, F3C3, Fp1F3, P3O1, T5O1, for other channels and subbands has not seen any significant changes with regard to average power spectral density. Conclusion: HG and normal pregnancies, when examined in terms of power spectral density, abnormalities were observed in the EEG signals in the left hemisphere frontal area of the delta band, fronto-centro-parietal, and parietal-occipital areas of the theta band. In light of the literature, neither cerebral abnormalities in HG could be displayed nor the place of abnormality could be shown. However, this study is the first to clearly show abnormalities of theta-delta band activity and differences of locations in the left cerebral hemisphere.