In this study we aimed to evaluate the role of closed-suction drainage on the extent of epidural fibrosis (EF) after lumbar disc surgery and to define a new grading system of epidural fibrosis in these patients, based on magnetic resonance imaging. Seventy-nine patients (34 women, 45 men) with a unilateral, single-level lumbar disc herniation were included in this study. Forty-one patients in whom closed-suction drainage was implanted were compared with 38 patients in whom the drain was not implanted. We have used a new grading system for the extent of epidural fibrosis, on the basis of follow-up magnetic resonance imaging findings. Pain intensity was evaluated by visual analog scale (VAS), and the patients' function and working ability were measured according to the Prolo functional-economic scale. We conclude that, in patients operated on for unilateral, single-level lumbar disc hernias, implantation of closed-suction drainage into the operation site results in less formation of EF radiologically and yields better clinical outcome.