As the field of hip arthroscopy continues to grow rapidly, our understanding of the population of patients undergoing hip arthroscopy has led to improved diagnosis and management of hip joint pathologies. The Multicenter Arthroscopic Study of the Hip (MASH) Study Group conducts multicenter clinical studies in arthroscopic hip preservation surgery. Patients undergoing arthroscopic hip preservation surgery are enrolled in a large prospective longitudinal cohort at 10 separate sites nationwide by 10 fellowship-trained hip arthroscopists. In this study, we collected epidemiologic data on the 1738 patients who enrolled between January 2014 and November 2016. These data include demographics, pathologic entities treated, patient-reported measures of disease, and surgical treatment preferences. Our study results showed that patients who elected hip arthroscopy were younger to middle-aged white females with pain primarily located in the groin region. Most had pain for at least 1 year, and it was commonly exacerbated by sitting and athletic activities. Patients reported clinically significant pain and functional limitation and a decrease in physical and mental health. It was not uncommon for patients to have undergone another, related surgery and nonoperative treatments, including intra-articular injection and/or physical therapy, before surgery. There was a high incidence of abnormal hip morphology suggestive of a cam lesion, but the incidence of arthritic changes on radiographs was relatively low. Labral tear was the most common diagnosis, and most often it was addressed with repair. Many patients underwent femoroplasty, acetabuloplasty, and chondroplasty in addition to labral repair.