Between 1986 and 1991, 14 patients (nine men and five women), ranging in age from 22 to 67 years (mean, 43 yr), presented with acute cauda equina syndrome from a herniated lumbar disc. All presented with bilateral sciatica and leg weakness; 13 (93%) had urine or stool incontinence, or both. At presentation, all were emergently studied with myelogram/computed tomographic or magnetic resonance imaging. Nine (64%) had large or massive herniations, including two with tethered cords. Five had smaller herniations superimposed on preexisting stenosis. Three had previous surgery; two-thirds had a herniation at a different level. The levels of the herniations were L4-L5 in nine patients, L5-S1 in three patients, and L3-L4 in two patients. The time to surgery ranged from less than 24 hours to more than 30 days; 11 patients underwent surgery within 5 days of onset. Follow-up ranged from 6 months to 5 years (mean, 3.3 yr). Postoperatively, six patients (44%) were normal, four (28%) had chronic pain and numbness, and four (28%) had persistent incontinence and weakness. All the patients were ambulatory. There were no operative deaths, and only one patient had a wound infection. Of the 10 patients who had no incontinence after surgery, 7 underwent surgery within 48 hours of onset. Of the four patients with persistent incontinence, all underwent surgery after 48 hours. Previous reports and our experience demonstrate the following most common characteristics for this presentation: 1) male sex; 2) L4-L5 herniations; and 3) onset in the 4th decade.(ABSTRACT TRUNCATED AT 250 WORDS)