BETWEEN JANUARY 1990 and February 1992, a total of 301 patients underwent discectomy for lumbar disc herniation; 29 had an extreme lateral herniation, i.e., foraminal or extraforaminal. The intervertebral foramen is a three-dimensional area demarcated primarily by the pedicles; we call it the lateral interpedicular compartment. The extraforaminal zone is the space outside the lateral border of the pedicles. All patients were evaluated by computed tomography (CT), water soluble myelography, postmyelographic CT scanning, or magnetic resonance imaging. Fifteen patients consecutively underwent disco-enhanced CT to adjust a correct diagnosis and to distinguish extraforaminal from foraminal herniation. In 10 cases of extraforaminal herniation, a selective radicular decompression with good-to-excellent clinical results was achieved by an extra-axial lateral decompression of the interpedicular compartment, with preservation of the facet joint. The operative target was the lateral aspect of the pars interarticularis and not the intertransverse space, as previously described. In two cases of both foraminal and extraforaminal herniation, the same technique was used. Fourteen patients with foraminal disc herniation and three patients with both foraminal and extraforaminal herniation underwent a standard intervertebral foraminotomy. An accurate preoperative diagnosis established by disco-CT is crucial in order to select the most suitable surgical approach.