The predictive value of quantitative electroencephalography (EEGq) was investigated with regard to the pharmacological treatment of 10 non-medicated obsessive-compulsive disorder (OCD) patients diagnosed according to DSM-IV criteria. The following variables were selected: bipolar relative power in alpha band for Cz-C3, Cz-C4, T3-T5, T4-T6, T3-F7 and T4-F8; bipolar relative power in theta band for Cz-C3, Cz-C4, T3-T5, T4-T6, T3-F7 and T4-F8; and monopolar relative power in theta band for Fp1, Fp2, F7, F3, Fz, F4 and F8. There was statistically significant deviations in five patients with regard to bipolar relative power in alpha band for central regions when compared to normative data bank (control group). This group of patients had a significantly lower age of OCD onset and worse response to pharmacotherapy with serotonin reuptake inhibitors.