Although epidural corticosteroid injections are commonly used for sciatica, their efficacy has not been established. In a randomized, double-blind trial, we administered up to three epidural injections of methylprednisolone acetate (80 mg in 8 ml of isotonic saline) or isotonic saline (1 ml) to 158 patients with sciatica due to a herniated nucleus pulposus. All patients had Oswestry disability scores higher than 20 (on a scale of 1 to 100, with scores of 20 or less indicating minimal disability, and higher scores greater disability). At three weeks, the Oswestry score had improved by a mean of -8.0 in the methylprednisolone group and -5.5 in the placebo group (95 percent confidence interval for the difference, -7.1 to 2.2). Differences in improvements between the groups were not significant, except for improvements in the finger-to-floor distance (P=0.006) and sensory deficits (P=0.03), which were greater in the methylprednisolone group. After six weeks, the only significant difference was the improvement in leg pain, which was greater in the methylprednisolone group (P=0.03). After three months, there were no significant differences between the groups. The Oswestry score had improved by a mean of -17.3 in the methylprednisolone group and -15.4 in the placebo group (95 percent confidence interval for the difference, -9.3 to 5.4). At 12 months, the cumulative probability of back surgery was 25.8 percent in the methylprednisolone group and 24.8 percent in the placebo group (P=0.90). Although epidural injections of methylprednisolone may afford short-term improvement in leg pain and sensory deficits in patients with sciatica due to a herniated nucleus pulposus, this treatment offers no significant functional benefit, nor does it reduce the need for surgery.