Objective To investigate the impact of joint capsule repair and external rotators suture on the prognosis in primary total hip arthroplasty (THA) by posterolateral approach. Methods Between January 2006 and June 2009, 159 patients with femoral neck fracture underwent primary THA by posterolateral approach, and were divided into 4 groups according to different treatments: joint capsule repair and external rotators suture were given in group A (n=38), only joint capsule repair in group B (n=39), only external rotators suture in group C (n=41), and no joint capsule repair or external rotators suture in group D (n=41). There was no significant difference in gender, age, cause of injure, disease duration, type of fracture, combined medical disease, or prosthesis selection among 4 groups (P gt; 0.05). The bleeding volume, drainage, postoperative hip dislocation rate, hip Harris score, and the hip range of motion (ROM) in internal rotation and external rotation were compared. Results There was no significant difference in operative time, bleeding volume, or drainage among 4 groups (P gt; 0.05). Postoperative hip dislocation occurred in 0, 0, 4 (9.8%), and 4 (9.8%) cases of groups A, B, C, and D, respectively, showing significant difference in incidence of postoperative hip dislocation among 4 groups (χ2=7.910, P=0.048). The hip Harris scores were significantly improved after operation when compared with preoperative scores in 4 groups (P lt; 0.05). Significant differences were found in hip Harris score at 6 weeks and 6 months after operation among 4 groups (P lt; 0.05); group D was significantly lower than groups A, B, and C, and groups B and C were significantly lower than group A (P lt; 0.05). There was no significant difference in the hip ROM in internal rotation among 4 groups at 6 weeks and 6, 12 months after operation (P gt; 0.05); but the hip ROM in external rotation were significantly bigger in groups A and C than in groups B and D at 6 weeks and 6 months after operation (P lt; 0.05). Conclusion Joint capsule repair and external rotators suture in primary THA by posterolateral approach do not increase the bleeding volume and drainage, but can reduce the early postoperative hip dislocation risk, increase the Harris score, and recover the external rotation function of involved hip. So joint capsule and external rotators should be repaired in THA by posterolateral approach.