BACKGROUND: Simultaneous rotator interval release is not classically performed during arthroscopic rotator cuff repair (RCR). However, concurrent rotator interval release has been anecdotally reported to facilitate less propensity for postoperative shoulder stiffness. The purpose of our investigation was to compare outcomes of pain and stiffness among patients who underwent arthroscopic rotator cuff repair with and without concomitant rotator interval release. METHODS: A single-blinded, randomized controlled trial was conducted between September 2018 and April 2021. Outcomes including Visual Analog Scale (VAS), narcotic usage, American Shoulder and Elbow Surgeons (ASES) Shoulder Score, active forward flexion (aFF), and active external rotation (aER) range of motion measurements were collected at 4-6 weeks, 3 months, 6 months, and at most recent follow-up postoperatively. RESULTS: 83 patients were prospectively enrolled and randomized into RCR with rotator interval versus without interval release. Postoperative temporal association between VAS score, ASES score, and average narcotic pain tablet use did not depend on group assignment (P = 0.990, P = 0.760, and P = 0.700, respectively). Similarly, the association between time point and aFF and aER range of motion did not depend on group assignment (P = 0.300 and P = 0.630, respectively). CONCLUSION: Arthroscopic rotator interval release during rotator cuff repair showed no statistically significant difference in short-term or long-term postoperative pain or range of motion outcomes compared to control.