Three patients who had a diagnosis of congenitally absent lumbar pedicle underwent CT examination. Findings showed that each patient had an aberrant hypoplastic pedicle plus a retroisthmic defect in the ipsilateral lamina rather than an absent pedicle. Axial CT was the diagnostic modality of choice; reformated images were of little value. The nature of the anomaly explains the difficulty in diagnosis by plain film radiography or tomographic study. The differential diagnosis to be considered from findings of plain film radiography includes pediculate thinning, neoplastic disease, neurofibroma, mesodermal dysplasia associated with neurofibromatosis, and vascular anomalies.