Functional-based resection under awake conditions had been associated with a nonnegligible rate of intraoperative and postoperative epileptic seizures. The authors assessed the incidence of intraoperative and early postoperative epileptic seizures after functional-based resection under awake conditions. The authors prospectively assessed intraoperative and postoperative seizures (within 1 month) together with clinical, imaging, surgical, histopathological, and follow-up data for 202 consecutive diffuse glioma adult patients who underwent a functional-based resection under awake conditions. Intraoperative seizures occurred in 3.5% of patients during cortical stimulation; all resolved without any procedure being discontinued. No predictor of intraoperative seizures was identified. Early postoperative seizures occurred in 7.9% of patients at a mean of 5.1 ± 2.9 days. They increased the duration of hospital stay (p = 0.018), did not impact the 6-month (median 95 vs 100, p = 0.740) or the 2-year (median 100 vs 100, p = 0.243) postoperative Karnofsky Performance Status score and did not impact the 6-month (100% vs 91.4%, p = 0.252) or the 2-year (91.7 vs 89.4%, p = 0.857) postoperative seizure control. The time to treatment of at least 3 months (adjusted OR [aOR] 4.76 [95% CI 1.38-16.36], p = 0.013), frontal lobe involvement (aOR 4.88 [95% CI 1.25-19.03], p = 0.023), current intensity for intraoperative mapping of at least 3 mA (aOR 4.11 [95% CI 1.17-14.49], p = 0.028), and supratotal resection (aOR 6.24 [95% CI 1.43-27.29], p = 0.015) were independently associated with early postoperative seizures. Functional-based resection under awake conditions can be safely performed with a very low rate of intraoperative and early postoperative seizures and good 6-month and 2-year postoperative seizure outcomes. Intraoperatively, the use of the lowest current threshold producing reproducible responses is mandatory to reduce seizure occurrence intraoperatively and in the early postoperative period.