This study was performed to evaluate the incidence of seizures with its implications on disease progression and the diagnostic value of post-ictal magnetic resonance images (MRI) during the management of high-grade gliomas (HGGs). A total of 406 consecutive patients with newly diagnosed HGGs were retrospectively reviewed. The incidence of seizures during the management was investigated. In patients who experienced a seizure, the causality between seizures and disease progression was assessed by pre-ictal, post-ictal (<1 month), and follow-up (<3 months) MRI. After a median follow-up of 17.4 months (range 0.1-88.3), seizures developed in 127 patients (31 %). Of the 127 patients, radiological progression at the post-ictal MRI was found in 83 patients (65 %) and the follow-up MRI confirmed progression in 79 patients (62 %). Four other patients (3 %) were shown to be progression-free. Among those without radiological progression at the post-ictal MRI, the follow-up MRI confirmed progression-free in 31 patients (24 %); however, 13 patients (10 %) revealed eventual progression. In the patients with a seizure, absence of preoperative seizures (p = 0.003), <95 % tumor resection (p = 0.001), and pre-ictal Karnofsky Performance Scale score ≤ 70 (p = 0.025) were significantly associated with disease progression. During the management of HGG, 31 % of patients experienced seizures; of these patients, 72 % harbored progressive disease. The post-ictal MRI is useful for detecting disease progression; however, there are pitfalls. Clinical settings should be considered together for diagnosing disease progression in patients with seizures.