Abstract:[Objective] To compare the clinical efficacy of T-shaped capsulotomy versus transverse capsulotomy in hip arthroscopy for treatment of the cam-type femoroacetabular impingement syndrome (FAI) . [Methods] A retrospective study was done on 70 patients who underwent arthroscopic surgery for cam-type FAI from July 2017 to June 2018. Among them, 35 patients had the capsule opened by Tshaped incision (the T-shaped group) , while the remaining 35 patients received transverse capsulotomy (the transverse group) . The periop- erative, follow-up and imaging documents were compared between the two groups. [Results] All patients in both groups had operation per- formed successfully without serious complications, such as injuries to important blood vessel and nerve. The T-shaped group proved signifi- cantly superior to the transverse group in terms of operation time and intraoperative fluoroscopy frequency (P<0.05) , although there were no significant differences in total incision length, intraoperative blood loss, time to recover ambulation and hospital stay between the two groups (P>0.05) . All patients in both groups were followed up for more than 24 months, with an average of (26.66±2.10) months. The VAS scores significantly decreased (P<0.05) , whereas the mHHS and iHOT scores significantly increased in both groups at the latest follow up compared with those preoperatively (P<0.05) . The T-shaped group had lower VAS score than the transverse group at the latest follow up, but the difference was not statistically significant (P>0.05) . However, the T-shaped group had significantly higher mHHS and iHOT-12 scores than the transverse group at the latest follow up (P<0.05) . Radiographically, the α angle and lateral center edge angle (LCEA) signifi- cantly reduced (P<0.05) , while the femoral head-neck offset (FHNO) significantly increased in both groups at the latest follow-up com- pared with those preoperatively (P<0.05) . The T-shaped group proved significantly superior to the transverse group in terms of α angle and FHNO at the last follow-up (P<0.05) , nevertheless, there was no a significant difference in LCEA between the two groups (P>0.05) . [Conclusion] Hip arthroscopy by T-shaped capsulotomy does achieve considerably better clinical outcomes than that by transverse capsulotomy for treatment of cam-type femoroacetabular impingement.