Even among skilled spinal deformity surgeons, neurologic deficits are inherent potential complications of spine surgery. The aim was to assess the meaning of changes and to evaluate the critical rates of Somatosensory Evoked Potentials (SEP) and Motor Evoked Potentials (MEP) for Neurologic Deficit (ND) occurrence associated with scoliosis surgery. A Group of 30 patients with idiopathic scoliosis treated surgically by posterior correction and stabilisation were included. Patients were matched by age, sex, aetiology, Cobb angle, and surgical criteria. Data on three planar scoliosis correction and concomitant (INM) alarms were compared. Radiographic assessment was performed from radiographs taken before surgery and just after it. The (INM) was performed with the use of ISSIS (Inomed) in every patients the same fashion. The average thoracic curve correction was 69.7% and lumbar 69.8%. The average preoperative Apical Vertebral Rotation was 23.5° for thoracic and 27.9° for lumbar curves and postoperatively 10.9° and 14.3° respectively. There was a significant variability of SEP during surgery with only 7 (23%) patients with stable SEP. 15(50%) patients had a decrease of SEP below 50% and 8(27%) had severe decrease of SEP below 50% what caused us to stop surgery or to decrease correction of curves. There was a MEP decrease in 11(37%) patients and in 6 (20%) directly after correction up to 50% of normal value. In 5 of 30 (17%) patients there was a significant decrease of MEP below 50% and we immediately released the implant. The SEP decrease up to 50% without any MEP change did not influenced the outcome. There was no correlation between flexibility and correction of the curve and SEP and MEP decrease. The safe level for MEP was not determined but its meaning for the outcome was more important than SEP value. The need of (INM) during scoliosis surgery to avoid (ND) was confirmed.