The purpose of this study was to evaluate the natural history of morphologic changes within the lumbar spine in patients who sustained lumbar disc extrusions. All patients in this study were treated nonoperatively for radicular pain and neurologic loss. The following questions were addressed: 1) Does perithecal or perineural fibrosis result when extrusions are not removed surgically, and 2) Do disc extrusions spontaneously resolve, and, if so, how rapidly? The study population consisted of 11 patients with extrusions and radiculopathy. All patients were successfully treated nonoperatively. All had a primary complaint of leg pain and all had positive straight leg raising reproducing their leg pain at less than or equal to 60 degrees. Additionally, 87% had muscle weakness on a neurologic basis in a root level distribution corresponding to the site of disc pathology. Computed tomographic (CT) examinations were obtained on all patients at the inception of treatment. These studies were compared with follow-up MRI studies. The initial CT scans were evaluated for the following criteria: disc size and position, thecal sac effacement, nerve root enlargement or displacement, and evidence of central or intervertebral canal stenosis. In addition to the pathomorphology evaluated on the CT scans, follow-up MRI studies also evaluated disc hydration at the herniated and contiguous levels, and the presence of perithecal or perineural fibrosis. The following grading system was used to evaluate change in fragment size on the follow-up studies: Grade 1-0 to 50% decrease in size; Grade 2-50 to 75% decrease in size; Grade 3-75 to 100% decrease in size.(ABSTRACT TRUNCATED AT 250 WORDS)