Pediatric convulsive seizure is common and represents a source of major concern and anxiety for the parents. Seizures can have a broad spectrum of etiologies in children, including metabolic, traumatic, developmental, and infectious causes. Depending on the clinical presentation, laboratory testing and neuroimaging may be indicated in the workup of the first unprovoked afebrile seizure. We present a case of a six-year-old boy who was brought to the emergency department by his mother after an episode of convulsion. She reported that he had jerky repetitive movements of all extremities that lasted around two minutes with spontaneous termination. The child did not have a febrile illness. The mother reported no history of similar episodes. Upon examination, the child appeared alert and conscious. No dysmorphic features were evident. Initial laboratory investigations were within the normal limits. The child underwent magnetic resonance imaging for the brain, which demonstrated a large well-defined extra-axial cystic lesion occupying most of the left hemisphere that is connected to the ventricular system. The lesion had no grey-matter lining and it strictly followed the cerebrospinal fluid in all sequences. Such finding represented the diagnosis of a giant left porencephalic cyst. Porencephaly is an extremely rare neurological anomaly that may present with pediatric seizures. Magnetic resonance imaging is the gold standard modality for the diagnosis of porencephaly. The case demonstrated that porencephaly can have a massive size in a patient with normal psychoneurological development.