In the 20-50-year age group, hip pain usually indicates dysplasia. Chronic mechanical pain is the usual pattern, although acute pain caused by avulsion or degeneration of the labrum may occur. The morphological characteristics of the dysplastic hip should be evaluated, and the link between the dysplasia and the osteoarthritis should be confirmed. Three factors indicate a favorable prognosis: joint space preservation, age younger than 40 years, and correctable femoral and acetabular abnormalities. Reconstruction is highly desirable, as it delays the need for joint replacement by 20 years. After 15 years, good outcomes are seen in 87% of patients after shelf arthroplasty and 85% after femoral varus osteotomy with or without shelf arthroplasty. Chiari acetabular osteotomy can be performed in patients with osteoarthritis but is followed by prolonged limping. Periacetabular osteotomy should be reserved for patients with moderate dysplasia and no evidence of osteoarthritis. Shelf arthroplasty and femoral osteotomy require 5-8 months off work (compared to 5 months after hip replacement surgery) but subsequently permits a far more active lifestyle. Hip replacement, which is required 20 years or more after biologic reconstruction, carries the same prognosis as first-line hip replacement (good results in 80% of patients after 15 years). Acute sharp pain related to anterior hip derangement also occurs in primary femoroacetabular impingement (FAI). The most common pattern is cam impingement, which is due to a decrease in head-neck offset and manifests as pain during flexion and adduction of the hip. Cam impingement can be corrected by anterolateral osteoplasty, which is often performed arthroscopically. Pincer-type impingement is contact between the anterior acetabular rim and the femoral neck due to retroversion of the proximal acetabulum. The imaging study strategy is discussed. Coxometry, computed tomography, and arthrography can be used. Primary FAI, which occurs as a result of geometric abnormalities, should be distinguished from secondary impingement. Causes of secondary impingement include exaggerated lumbar lordosis with pelvic tilt and to hip osteophytosis (sports or posterior hip osteoarthritis). Osteoplasty is rarely appropriate in patients with secondary impingement. The features of acute anterior hip derangement are now better defined. They can be used to guide palliative treatment, which is effective, in the medium term at least. Experience acquired over the last two decades has established the efficacy of surgery for hip dysplasia.