Anatomic studies using cadavers showed that three factors are responsible for radicular symptoms. The first is congenital or acquired abnormalities of nerves and nerve roots—the intradural segmental arrangement of rootlets, congenital anomalies of the nerve roots, and the furcal nerve. Another factor is changes of bone and soft tissue around nerves and nerve roots—indentation of nerve roots and extremely transverse courses of nerve roots. The third factor Is a correlation of two other factors—spatial relationship of the nervous tissue to osseous and nonosseous elements of the spinal canal and the intervertebral foramen. In the intervertebral foramen, the nerve root is surrounded by a rather thick membranous structure, an epiradicular sheath, which is responsible for a tubular form obtained in nerve root Infiltration. Anatomic abnormalities can be observed In contrast studies, but the defects revealed do not correspond necessarily with neurologic symptoms. In such cases, nerve root Infiltration Is very useful for a functional diagnosis. The analysis of radicular symptoms with nerve root Infiltration showed that radicular pain and/or claudication are caused mainly by single nerve root involvement, irrespective of the findings obtained by contrast studies. Furthermore, therapeutic effect of nerve root infiltration can be expected in any disease and it can be applied as a final trial of conservative treatment.