The treatment of thoracic adolescent idiopathic scoliosis (AIS) of more than 80 degrees traditionally consisted of a combined procedure, an anterior release performed through an open thoracotomy followed by a posterior fusion. Recently, some studies have reassessed the role of posterior fusion only as treatment for severe thoracic AIS; the correction rate of the thoracic curves was comparable to most series of combined anterior and posterior surgery, with shorter surgery time and without the negative effect on pulmonary function of anterior transthoracic exposure. Compared with other studies published so far on the use of posterior fusion alone for severe thoracic AIS, the present study examines a larger group of patients (52 cases) reviewed at a longer follow-up (average 6.7 years, range 4.5-8.5 years). The aim of the study was to evaluate the clinical and radiographic outcome of surgical treatment for severe thoracic (>80 degrees) AIS treated with posterior spinal fusion alone, and compare comprehensively the results of posterior fusion with a hybrid construct (proximal hooks and distal pedicle screws) versus a pedicle screw instrumentation. All patients (n = 52) with main thoracic AIS curves greater than 80 degrees (Lenke type 1, 2, 3, and 4), surgically treated between 1996 and 2000 at one institution, by posterior spinal fusion either with hybrid instrumentation (PSF-H group; n = 27 patients), or with pedicle screw-only construct (PSF-S group; n = 25 patients) were reviewed. There were no differences between the two groups in terms of age, Risser's sign, Cobb preoperative main thoracic (MT) curve magnitude (PSF-H: 92 degrees vs. PSF-S: 88 degrees), or flexibility on bending films (PSF-H: 27% vs. PSF-S: 25%). Statistical analysis was performed using the t test (paired and unpaired), Wilcoxon test for non-parametric paired analysis, and the Mann-Whitney test for non-parametric unpaired analysis. At the last follow-up, the PSF-S group, when compared to the PSF-H group had a final MT correction rate of 52.4 versus 44.52% (P = 0.001), with a loss of -1.9 degrees versus -11.3 degrees (P = 0.0005), a TL/L correction of 50 versus 43% (ns), a greater correction of the lowest instrumented vertebra translation (-1.00 vs. -0.54 cm; P = 0.04), and tilt (-19 degrees vs. -10 degrees; P = 0.005) on the coronal plane. There were no statistically significant differences in sagittal and global coronal alignment between the two groups (C7-S1 offset: PSF-H = 0.5 cm vs. PSF-S = 0 cm). In the hybrid series (27 patients) surgery-related complications necessitated three revision surgeries, whereas in the screw group (25 patients) one revision surgery was performed. No neurological complications or deep wound infection occurred in this series. In conclusion, posterior spinal fusion for severe thoracic AIS with pedicle screws only, when compared to hybrid construct, allowed a greater coronal correction of both main thoracic and secondary lumbar curves, less loss of the postoperative correction achieved, and fewer revision surgeries. Posterior-only fusion with pedicle screws enabled a good and stable correction of severe scoliosis. However, severe curves may be amenable to hybrid instrumentation that produced analogous results to the screws-only constructs concerning patient satisfaction; at the latest follow-up, SRS-30 and SF-36 scores did not show any statistical differences between the two groups.