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Real neurological findings in 177 cases of lumbar disc hernia, the levels of which were operatively proved were compared with those described as corresponding to a certain level of hernia in books hitherto published. Sensory change in Keegan's L5 dermatome was accordant with L4-5 hernia only in 41%, that in S1 dermatome with L5-S1 hernia in 44%, and that in L4 dermatome with L3-4 hernia in 67%. Weakness of an entire lower limb or of lliopsoas was proved in accordance with L1-2 or L2-3 hernia. However, weakness of extensor hallucis longus with L4-5 hernia only in 65%, that of flexor hallucis longus with L5-S1 hernia in 37%, and that of quadriceps with L3-4 hernia in 44%. Patellar tendon reflex was diminished in 67% of L3-4 hernia, in 10% of L4-5 hernia, and in 6% of L5-S1 hernia. However, since the incidence of L4-5 hernia was much higher than L3-4 hernia, this finding was encountered in L4-5 hernia as often as in L3-4 hernia. By the same reason, diminished Achilles tendon reflex was encountered in L4-5 hernia as often as in L5-S1 hernia. Findings above described together with consideration that the positional deviation of a disc hernia at a certain lumbar intervertebral level did not cause simultaneous compression on a nerve root which branched at the level of herniation and one which branched one level above it, disclosed an individual difference in motor and sensory innervation was so great that a lumbar disc hernia at a certain level coincided with hitherto described neurological findings only in 40 to 60%. Results of this study led to the conclusion that the level of lumbar disc hernia could not be determined only with neurological findings but with myelography and other figure analyses.