Category: Arthroscopy; Ankle; Hindfoot; Sports Introduction/Purpose: Haglund's syndrome is a common cause of posterior heel pain and can be associated with retrocalcaneal bursitis and degenerative Achilles tendinosis. Open approaches for resection of the Haglund's lesion have long been employed in patients that fail to improve with conservative treatment. This often involves partial elevation of the Achilles insertion with reattachment. More recently, endoscopic surgical techniques have evolved, enabling more rapid rehabilitation with less tendon disruption. The decision on the surgical approach is influenced by the degree of insertional Achilles tendinosis with endoscopic techniques preferred in the absence of insertional pathology. The primary objective of this investigation was to report on a large series of patients treated surgically for symptomatic Haglund's lesions. Methods: We reviewed the outcomes of Haglund's syndrome surgical cases at our institution over a five-year period. We included cases with insertional Achilles tendinosis and retrocalcaneal bursitis related to the Haglund's lesion, but excluded revisions and cases involving flexor hallucis longus tendon transfers. We recorded patient demographics, sport and activity level, comorbidities, BMI, duration of symptoms, surgical technique, tourniquet time, rehabilitation protocol, postoperative complications, and duration of postoperative follow-up. We also reviewed relevant preoperative imaging and recorded the presence of Achilles insertional degenerative calcification or an insertional calcaneal enthesophyte on radiographs. We then prospectively administered questionnaires regarding return to sport and patient-reported outcome measures including the SANE, PASS, VISA-A and PROMIS (Physical Function, Pain Interference and Global Health domains). Results: In total, 17 of the 77 (22%) included cases were performed with the endoscopic surgical technique. Six patients underwent bilateral Haglund surgeries during the study period, accounting for 12 of the 77 cases. The open Haglund resection group had a higher rate of concomitant Achilles insertional degenerative calcification on radiographs and MRI (72%). In addition, the open group was older than the endoscopic group (average age 54 vs 45), had a higher rate of comorbidities, higher rate of postoperative complications, and a higher rate of return to the operating room for revision surgery (11% vs 0% for endoscopic). Seventeen patients were elite distance running athletes and were preferentially treated by endoscopic techniques (11/17, 64%). At 24-month follow-up, the majority of patients report return to baseline activity. Conclusion: Patients treated surgically for Haglund's syndrome and insertional Achilles tendinopathy generally have good outcomes. Outcomes are better for endoscopically treated patients compared to open treatment, although these patients tend to be younger, healthier, and have less Achilles tendons disease. Still, some degree of Achilles tendinopathy and limited intrasubstance calcification can be successfully addressed with the endoscopic technique. We are endeavoring to better define indications for, and limitations of, the endoscopic technique for insertional Haglund's disease.