This paper reports on three cases of an intradural lumbar disc herniation (IDLDH) that were diagnosed by a radiological examination. In all cases, an intradural vacuum (IDV) was detected on the CT scans, and the IDLDH showed iso- or lower signal intensity on the T2-weighted images. Enhanced MRI of one case revealed a small amount of air, but this was without enhancement. All the cases showed definite IDV on the CT scans, and this was an important clue for diagnosing IDLDH.