The authors describe the clinical observation of a patient with a paraventricular tumor of the left frontal lobe and demonstrate the effectiveness of endoscopic biopsy of a volumetric mass of such localization through the lateral ventricle using intraoperative navigation. The disease manifested with convulsive seizures two years before the patient was admitted to the hospital. During this period of time, he was repeatedly examined. The dimensions of the volumetric formation remained unchanged. Based on the data obtained, it was not possible to accurately verify the type of tumor. Anticonvulsant therapy was ineffective. The patient underwent surgery — endoscopic partial removal of the tumor (biopsy) and opening of the tumor cyst through the left lateral ventricle using intraoperative navigation. Clinical improvement in the patient’s condition was achieved. After the operation, the headaches and the seizures stopped.