Endoscopy has a long history and is used extensively today following recent technical improvements. Endoscopy has been used in neurosurgery to examine ventricles, cisterns, and intra-arteries. In this study, we evaluated the possibility of endoscopic examination and treatment in the narrow confines of the subarachnoid space of the spine and the posterior fossa. Endoscopes with external diameters of 0.5, 1.4, and 2.2 mm were used. While the first two endoscopes had rigid tips, the 2.2-mm endoscope had a directable tip. Each endoscope was inserted percutaneously in the lumbar region in five cadavers and was advanced cranially into the posterior fossa under endoscopic monitoring. Arteries, veins and nerve roots upon the surface of the spinal cord could be distinguished readily with all endoscopes. All endoscopes could be inserted under direct observation, avoiding these vessels and nerve roots. Further rostral advancement of the endoscope permitted visualization of the upper spinal cord, cisterna magna at the foramen magnum, and the fourth ventricle. The lower aspect of the cerebellum, the foramen of Magendie, and the cerebral aqueduct could be observed from below. When the endoscope was advanced ventrolaterally, the vertebral artery and lower cranial nerves were observed. From this preliminary cadaver study, endoscopy via lumbar puncture appeared useful for inspection of structures surrounding the spinal cord and posterior fossa, and for some simple treatments.