OBJECTIVES: Latissimus dorsi tendon transfer is a treatment option in patients with irreparable rotator cuff tears. This study aimed to compare the effectiveness and safety of anterior and posterior transfer of latissimus dorsi tendon for anterosuperior or posterosuperior massive irreparable rotator cuff tears. METHODS: In this prospective clinical trial, 27 patients with irreparable rotator cuff tears were treated with latissimus dorsi transfer. The transfers in 14 and 13 patients were from the anterior for anterosuperior cuff deficiency (group A) and from the posterior for posterosuperior cuff deficiency (group B), respectively. Pain, shoulder range of motion in forward elevation, abduction, external rotation, and functional scores were evaluated 12 months after the surgery. RESULTS: Two and one patients were excluded from the study due to not referring in time for follow-up and infection, respectively. Therefore, 13 patients remained in group A and 11 patients in group B. Visual analog scale scores decreased from 6.5 to 3.0 in group A (P=0.016) and from 5.909 to 2.818 in group B (P=0.028). The constant scores improved from 41 to 50.2 (P=0.010) in group A and from 30.2 to 42.5 (P=0.001) in group B. There was a significant improvement in the abduction and forward elevation in both groups which was more significant in group B. The posterior transfer made significant improvement in external rotation; however, the anterior transfer did not change external rotation. No radial or axillary nerve injury was observed in any of the two groups. CONCLUSION: Latissimus dorsi transfer in patients with irreparable rotator cuff tears has a significant effect on recovery. It improves shoulder function and range of motion and reduces pain. Improvement of shoulder elevation and abduction is more significant in posterior transfer. The anterior transfer is as safe as the posterior transfer for nerve injury.