Out of a series of 1850 cases operated upon for lumbar disc herniation 130 underwent re-operation because of persistent or recurrent symptoms. Re-operation was successful in 62%. The prognosis of re-operation was not related to special clinical symptoms and signs but only to the operative findings. Herniations at other levels and recurrences of lumbar disc herniations had the best results (excellent in 98% respectively 54%), but scar formations alone came out much less satisfactory (only 38% excellent results). Computed tomography (CT) findings were less reliable in distinguishing between disc prolapse and fibrosis than magnet resonance imaging (MR). Therefore MR is the diagnostic method of choice in these conditions, and scar formations alone should be considered a contra-indication for re-operation.