To determine the efficacy of an open posterior capsulolabral reconstruction (PCLR) with a posterior deltoid-saving approach, 30 PCLRs in 29 patients with unidirectional posterior instability were reviewed retrospectively. The mean follow-up period was 30 months (range, 25-59 months). Posterior capsular redundancy was observed in all cases, but a posteroinferior labral tear was found in only 5. Posterior capsular thinning developed in 6 patients. According to the Rowe scale, 24 shoulders were rated as excellent, 1 as good, 2 as fair, and 3 as poor. The modified American Shoulder and Elbow Surgeons score at last follow-up was 91. During follow-up, recurrence of instability was observed in 4 cases, including 3 cases of voluntary instability. The overall recurrence rate was 13.3%, but the success rate was 92.6% when cases of voluntary instability were excluded. Whereas the midterm clinical results of PCLRs were satisfactory, the risk of recurrence was very high in patients with voluntary posterior instability, even though some subjective improvement could be obtained through a PCLR.