The authors retrospectively reviewed a series of 18 hard thoracic herniated discs (HTHD) operated by thoracoscopy. Isolated cases of HTHD have been reported in the literature, but no series describing these lesions has been published. Seventy-two percent of the herniated discs were situated between T8 and T12. Fifty-six percent of the patients had radiographic sequelae of Scheuermann's disease. Postoperatively, 83% had neurological improvement. In seven cases (39%), a plane separating the herniated disc and the dura mater was found surgically. In 11 patients, no separating plane was found during surgery. The lesion was intradural in three patients (17%) and adherent to the dura mater in eight (44%). Among these 11 patients, surgery was complicated by a dural tear in the first seven that led to a high risk of cerebrospinal fluid fistula: four of these seven patients had required surgical revision. In the last four, the zone of adhesion of the HTHD to the dura mater was preserved, successfully preventing dural tear Keywords Calcified thoracic disc herniation AE MRI AE Scheuermann AE Thoracic spine AE Thoracoscopy Eur Spine J (2006) 15: 537-542