Objective: Percutaneous endoscopic disc surgery on the lumbar spine evolved based on 2 major surgical principles: "inside-out" and "outside-in." The primary goal of this study was to apply a modified version of the inside-out technique whenever possible in patients with symptomatic thoracic disc herniation. Methods: The transforaminal approach is based on the target point in the midline of the posterior fifth of the disc, while the target point of the posterolateral approach is the center of the disc and the starting point for the modified inside-out technique, which is described as "the foraminal retreat" maneuver. In all cases, the operation started with the inside-out maneuver. In some cases where an accurate approach to the disc herniation was impossible, we also performed a foraminoplasty. Results: We surgically treated the 29 patients described in this case series, using a specially designed and access-optimized percutaneous endoscopic system on the thoracic spine. The visual analogue scale score for back and radicular pain decreased from 8.4 to 2.9. The overall satisfaction rate according to the MacNab criteria was 65% for excellent and good clinical outcomes at the latest follow-up, at a mean of 27 months (range, 2–67 months). Conclusion More than 80% of cases involving hard or soft thoracic disc herniation could be treated in the modified inside-out maneuver alone with percutaneous endoscopic transforaminal discectomy. The low complication rates of full-endoscopic spinal cases and surgical experience should always be kept in mind. The rarity of this pathology hinders the analysis of large case series and homogeneous cohorts in clinical studies.