Since its introduction in the neurosurgical field, neuroendoscopy has played an important role in the treatment of pineal germ cell tumors. The authors report a case of pineal germinoma revealing spontaneous regression before neuroendoscopic surgery. A 15-year-old boy presented with chronic headache, deterioration of his visual acuity, and diplopia. Head magnetic resonance imaging (MRI) revealed a large tumor in the pineal region and triventricular hydrocephalus due to occlusion of the aqueduct. As levels of tumor markers in serum and cerebrospinal fluid, including those of alpha-fetoprotein, carcinoembryonic antigen, human chorionic gonadotropin (hCG), and the beta-subunit of hCG, were all within the normal ranges, endoscopic surgery for biopsy and third ventriculocisternostomy was performed. Under endoscopic view, the tumor was revealed to be smaller than expected from preoperative images. MRI obtained 14 days after admission disclosed marked shrinkage of the tumor. The histopathological diagnosis was pure germinoma, and the patient underwent chemotherapy combined with fractionated radiotherapy. The tumor disappeared, and the patient did not show any signs of relapse. Spontaneous regression is a very rare phenomenon in malignant brain tumors, and in the literature it has been uncommonly described in pineal germ cell tumors. Our case disclosed a pitfall of modern strategy for this pathology with neuroendoscopy. Dilated ventricles and a certain amount of lesion are factors for safe endoscopic biopsy of pineal tumors. Radiographic images shortly before surgery are warranted, especially in patients whose symptoms of intracranial hypertension have already improved before surgery.