A contralateral neurologic deficit following microendoscopic discectomy (MED) or laminectomy (MEL) had not previously been reported. Between September 1999 and April 2004, 60 patients with symptomatic lumbar disc herniations or spinal stenotic syndrome received MED or MEL at the authors' institution. Three out of 60 patients were found to exhibit a contralateral neurologic deficit following unilateral microendoscopic surgery. All three patients complained of a newly developed, contralateral neurologic deficit following their operations. One MED patient with a concomitant contralateral disc herniation developed contralateral motor and sensory deficits and required immediate open surgery. At the two-year follow-up, a residual motor deficit was noted. The other two patients (1 MED, 1MEL) with temporary sensory deficits were only treated conservatively and experienced complete recovery one week and six weeks following the operation, respectively. Surgeons should pay close attention to the possibility that contralateral neurologic deficits may occur following MED or MEL. Our reports indicate that caution should be exercised when performing microendoscopic procedures on patients with substantial dural compromise, a concomitant contralateral disc herniation, or a lateral spinal stenosis, which may be etiologies.