We report a case of congenital lumbosacral limb duplication at the pelvis, lower limb, and foot of a 4-year-old boy. The patient presented with a supernumerary lower limb joined at the lumbosacral region by a bony connection. A pseudo-navel and a pseudo-penis were found on the supernumerary limb and foot duplication was noted at the end. Radiography and a 3-dimensional computed-tomography reconstruction revealed duplication of an inversely oriented pelvis dorsal to the normal pelvis, semi-vertebrae in T7 to T9, thoracolumbar scoliosis, lumbosacral vertebral dysplasia, and dislocation of the left hip. Magnetic resonance imaging demonstrated a tethered spinal cord and an adipoma in the sacral canal. Motor conduction velocity was reduced in the left peroneal nerve. Surgery to remove the supernumerary limb was successfully performed. The patient recovered well and further surgery is planned for functional reconstruction of the left lower limb.