In 2007, a patient with a herniated lumbar disc was admitted to the bed under my supervision. His symptoms and signs were more obvious. Moreover, he had been seen at the Downtown Hospital before coming to our hospital, and the orthopedic surgeon there had performed a CT examination of his lumbar spine. No obvious abnormality was mentioned. Later, he came to our outpatient clinic and underwent CT examination again. After admission, only a large herniated disc was noted on film review. He was given dehydrating and decongestant drugs and lumbar physiotherapy and traction. The patient’s symptoms were not significantly relieved. In response to the ineffective treatment, I later found, after careful review of CT films, that the patient had poorly visualized nerve roots on the left side of the L5/S1 intervertebral space, and that there was a mass-like faint shadow on the medial side. This was considered to be a prolapsed nucleus pulposus (see Figure 1). The patient was recommended to undergo MRI. Posterior MRI confirmed herniated discs in L3/4 and L4/5. The L5/S1 disc was prolapsed and the nucleus pulposus was prolapsed about 1 cm posteriorly and inferiorly to the left (see Figure 2). Based on the MRI findings, the patient was recommended to undergo surgery. The left side of the L5 lamina was opened surgically, and the ligamentum flavum was resected after opening the window with a small bone chisel. The nerve root on the left side of L5 was immediately visible, with significant edema and adhesions to the posterior longitudinal ligament inferiorly and anteriorly. The nerve roots were explored superiorly and anteriorly, and no detached nucleus pulposus tissue was seen. The nerve root was later reexamined medially and in the axillary region. A complete nucleus pulposus of approximately 1 cmx1cmx1cm was found to be adherent to the nerve root. The nucleus pulposus was completely removed after stripping (see Figure 3). There was no compression around the nerve root and a rupture in the posterior longitudinal ligament was seen. The patient’s symptoms and signs were typical, but I was not careful in my treatment, so I should have performed an MRI within three days before the patient’s admission. Special attention to detail should be paid in the future. We should improve our diagnosis and treatment.