Twenty-one consecutive patients (27 lumbar discs) were treated by percutaneous discectomy for lumbar herniated disc disease from July 1988 through March 1989. Twenty-six discs in 20 patients were evaluated with preoperative and postoperative magnetic resonance images graded by a neuroradiologist blinded to the clinical and prior imaging results. Fifteen patients were treated by one-level percutaneous discectomy and six patients by two-level percutaneous discectomy. The disc herniations were graded with respect to size, type, location, and hydration status on the magnetic resonance image scans. The postoperative magnetic resonance images were obtained 2–6 months after percutaneous discectomy. Early clinical outcomes after percutaneous discectomy were compared with the various magnetic resonance imaging parameters. Overall, treatment for thirteen patients (62%) was considered clinically successful (decrease or elimination of pain) after percutaneous discectomy, whereas treatment for eight (38%) patients was considered to clinically fail (persistence of pain) with follow-up ranging from 1 to 6 months postoperatively. Three of the patients in whom treatment failed have been subsequently treated successfully by laminotomy and discectomy. On the average, there is a small absolute decrease (5% of the anteroposterior diameter of the spinal canal) in the size of disc herniations when treated by percutaneous discectomy. Although this study is limited by a small sample size and lacks statistical significance, it appears that an early clinical success after percutaneous discectomy may be related to a few magnetic resonance imaging parameters. Early successful outcome appears more likely in a patient with a type II disc herniation [protrusion/bulge) and a disc herniation that has been shown to decrease in absolute size by greater than 10% of the anteroposterior diameter of the spinal canal from preoperative to postoperative (for exmaple, if a disc herniation measured 38% preoperatively and 28% postoperatively, the absolute change in size is 10%).