We retrospectively reviewed the myelograms of 433 patients and identified those who had no symptoms or signs referable to the thoracic cord, roots, or nerves. By post-myelography computed tomographic scan criteria, our frequency of asymptomatic thoracic herniated discs (ATHDs) was calculated. Post-myelography computed tomographic scans of 68 ATHDs were analyzed. Their imaging characteristics were compared with our own series of 5 symptomatic thoracic herniated discs and symptomatic thoracic herniated discs in the literature. We were unable to identify any imaging features that could reliably classify a disc as an ATHD or a symptomatic thoracic herniated disc. Our results call into question the propriety of prophylactic surgery for ATHDs, even when the lesions are radiographically impressive.