Aim:Epilepsy surgery is an effective treatment in patients suffering from refractory epilepsy. In this study, the aim is to discuss seizure outcomes of patients, who had had invasive EEG monitorization (IEM), following their epilepsy surgery at our centre. Material and Methods:Forty-seven patients suffering from refractory epilepsy and who were evaluated by invasive EEG were included in this retrospective study at Istanbul Faculty of Medicine from 2003 to 2017. We examined the Video EEG and invasive EEG monitorization, cranial MRI, SPECT, PET and neuropsychological tests of all patients. Moreover, postoperative seizure outcome results were evaluated according to Engel classification. The factors affecting seizure outcome were discussed. Results:Twenty-six of the patients were female (55.3%), 21 were male (44.7). The average age were 32.0 (±12.4). Forty-three patients had surgery and the average age of these patients was 26,6 (±11,15). 38.3% of the patients had hippocampal sclerosis (HS), 23.4% had focal cortical dysplasia (FCD), 8.5% had tumor, 14.9% had sequela lesion and 14.9% had unknown etiology. Postoperative seizure status according to the Engel classification showed that 81.6% of the patients were class I, 10.5% were class II, 2,6% were class III and 5,3% were class IV. Conclusion:A significant relation was statistically determined between structural MRI lesion and favorable seizure outcome (p<0.05). The most frequent etiology was HS in our patients. Of the patients with Engel I, the averages of their ages, ages at onset of epilepsy and ages at surgery were lower than other groups; but the difference was not statistically significant (p>0.05). We argue that IEM is an essential examination for favorable outcome for the determination of epileptogenic zone and/or the proximity of the functional structures.