Developmental anomalies of the lumbar spine are common. The disc between anomalous segments has a characteristic appearance on sagittal T2 MR images, not previously described. These have been classified into two types: transitional (where there is only partial fusion of bony segments), or rudimentary (where there is complete fusion of the two adjacent vertebral bodies). Both types produce discs that are smaller than adjacent, normal, mobile, lumbar disc segments. Disc signal intensity, from the anomalous segment, is normal, but the disc lacks an intranuclear cleft. Consideration of these appearances allows identification and differentiation from the normal, mobile lumbar disc in the absence of plain radiographs. Knowledge of such discs permits the application of accurate nomenclature to disc abnormalities above anomalous levels.