STUDY DESIGN: Retrospective study of clinical experiences. OBJECTIVES: The correct discrimination of a compressed root is very important for proper decompression. With a foraminal disc herniation, the cephalad root is compressed. The diagnostic importance of the clinical and radiological findings was investigated. SUMMARY OF LITERATURE REVIEW: A compressed root, due to a herniated disc, is known as a caudal root (i. e. L5 root compressed by L4-5 disc herniation). In some cases, a prolapsed disc may compress the cephalad root, resulting in a difficult diagnosis. MATERIAL AND METHOD: The medical records, plain X-ray and MRI of 17 patients were reviewed, and the physical examination and MRI findings were carefully evaluated to retrospectively document the efficacy of the diagnoses. Every MRI image of each patient was graded according to the 4 point ranking system of diagnostic efficacy devised by the authors. The clinical outcomes and postoperative complications were also investigated. RESULTS: Ten, 5 and 2 of the 17 patients had L4-5, L5-S1 and L3-4 foraminal disc herniations, respectively. Eight of 10 L4-5 cases showed a positive femoral nerve stretching test. The knee jerk reflex was diminished in 7 patients, with bilateral hyporeflexia in the other 3. The body-cut axial MRI image was the most effective, and the coronal images were also very helpful, whereas the routine axial images were of least value. Most cases achieved a satisfactory clinical result. CONCLUSIONS: Foraminal disc herniations seem to be reasonably common. For the accurate discrimination of a compressed root, a thorough physical examination seems to be very important. When MRI is performed for these cases, in addition to routine studies, the body-cut axial and coronal MRI images are effective and useful, and their use is strongly recommended.