Although osteochondroma is the most common benign bone tumor, the lumbar spine is anuncommon localization for solitary osteochondroma. Solitary lumbar osteochondromas rarely affect the neurological structures, because most of the lesions grow out of the spinal canal. We report a 48-year-old patient suffering from right foot-drop due to acute compression of right L4 nerve root by a lesion expanding into the spinal canal, originating from the right inferior articular facet of the third lumbar vertebrae. The symptoms improved after surgical removal of the lesion and histopathological examination of the lesion confirmed the diagnosis of osteochondroma. To the best of our knowledge, this is a unique case report in the literature.