A 5-month-old boy presented with a rare case of intramedullary teratoma extending from T1 to S5 and associated with a lumbosacral lipoma. Magnetic resonance imaging showed the tumor extended over the lipoma. Since the tumor could not be clearly demarcated from the spinal cord, surgery was performed under a preoperative diagnosis of spinal glioma. The lack of demarcation made safe resection of the tumor difficult to perform, so that the tumor was only partially removed by decompressing the spinal cord. The histological diagnosis was mature teratoma. This case was likely the result of some dysembryogenetic mechanism and the tumor was not neoplastic. The long-term outcome cannot yet be determined, but no recurrence of the symptoms has been observed for 3 years. Spinal intramedullary teratoma is rare and tends to be located in the lumbosacral region. Surgical intervention is crucial and total removal may be achievable, but is likely to be partial with tight adhesion to the spinal cord, so that aggressive approaches should be avoided in such cases.