Background: We have developed a novel technique for managing rotator cuff calcific tendonitis, involving arthroscopic debridement of calcific tendonitis with localization assistance from a breast biopsy needle under ultrasound guidance. While we have demonstrated encouraging results at six-month follow-up, the medium-term outcomes and the long-term outcomes of this technique at 2 years or beyond are unknown. The aim of this paper was to determine if this technique was successful in resolving symptoms after two years and beyond. Study Design: Retrospective Cohort Study. Methods: Patients who underwent arthroscopic debridement of calcific tendonitis with localization assistance from a breast biopsy needle under ultrasound guidance by a senior surgeon were evaluated using patient-rated pain scores and functional status with the use of the Likert scales and via examiner-rated shoulder range-of-motion and strength at the pre-operative visit, at 1, 6, 12, and 24 weeks post-operatively, and long-term at a mean of 249 weeks after surgery. Results: At a mean follow-up period of 4.8 years (range, 2–10 years), 31 patients (33 shoulders) experienced significant improvement in the severity of pain at rest, with overhead activities, and during sleep compared to their pre-operative presentation (p < 0.001). The patient experienced less frequent pain during activities and sleep, and a decreased frequency of extreme pain (p < 0.001). Passive range of abduction (p = 0.003), forward flexion (p < 0.001), and supraspinatus strength (p = 0.018) improved compared to the presurgical presentation. Out of 27 patients, 24 patients (89%) had complete resolution of calcific tendonitis, and 26 patients (96%) had an intact rotator cuff. Conclusion: Arthroscopic debridement of calcific tendonitis with localization assistance from a breast biopsy needle under ultrasound guidance was very effective. Patients had significant pain relief, improved range of motion, and a reduction in stiffness at a mean post-operative period of 4.8 years. Patients had a significant reduction in residual calcification, and rotator cuff integrity was largely preserved by long-term follow-up. What is known about this subject: Calcific tendonitis of the rotator cuff is one of the most painful and debilitating disorders of the shoulder. This condition is characterized by the deposition of calcium-phosphate crystals within the rotator cuff tendons. Arthroscopic debridement and excision of rotator cuff calcifications have proven to be efficacious treatments with regards to clinical and functional outcomes in the short and medium term. Identifying the calcific lesion intra-operatively, however, can prove to be challenging. Furthermore, inadequate excision of the calcific deposit has been shown to have poorer clinical outcomes. We designed a technique that utilizes the assistance of ultrasound to guide a localization-biopsy wire to the calcific lesion. This technique aids in precisely identifying the location of the lesion intra-operatively to optimize accuracy in removing the maximum amount of calcific deposit possible. A short-term follow-up study by us has demonstrated successful outcomes with regards to the return of function and relief of pain. However, there have been no studies evaluating the effectiveness of this particular technique beyond six months. What this study adds to current knowledge: At a mean of 4.8 years, arthroscopic debridement of calcific tendonitis, using our technique, was successful in relieving the severity and frequency of pain with overhead activities, pain at rest, and pain during sleep, as well as improving range of motion.