A 29-year-old man presented with a rare case of far-out foraminal stenosis with radiculopathy caused by osteophyte formation secondary to an anomalous articulation between the transverse process and the sacral ala. Diagnosis of unilateral far-out foraminal entrapment of the L5 spinal nerve below a transitional vertebra (TV) depended on selective radiculography and nerve root block. Computed tomography after selective radiculography clearly demonstrated foraminal entrapment of the L5 nerve root via the osteophytes. The patient underwent posterior decompression by resection of the osteophytes using an operating microscope and experienced good relief of radicular pain. This case illustrates the effectiveness and some refinements of posterior decompression for radicular pain caused by far-out foraminal stenosis below a TV and compression of the L5 spinal nerve.