Background: Significant controversy exists regarding the causes of premature, natural hip-joint failure. Identification of these causes may guide future investigations targeting prevention of this disorder. The aims of this study were to: (1) determine and characterize structural abnormalities associated with premature, natural hip-joint failure, and (2) analyze disease progression in the contralateral hips of patients with femoroacetabular impingement deformities. Methods: We analyzed 604 patients (710 hips) from three different medical centers who underwent primary total hip arthroplasty at or before fifty years of age (average age, forty years). Three hundred fourteen patients (52%) were male, and 290 patients (48%) were female. Results: The diagnoses associated with premature hip failure varied, but osteoarthritis and osteonecrosis were most common. Radiographic abnormalities associated with developmental hip dysplasia and femoroacetabular impingement were associated with the majority of osteoarthritic hips. Hips with femoroacetabular impingement deformities demonstrated distinct structural anatomy relative to asymptomatic hips, with a high prevalence of bilateral deformities. In a subgroup of seventy patients with femoroacetabular impingement deformities, contralateral radiographic disease progression or the need for total hip arthroplasty was observed in 73% of hips. Conclusions: Osteoarthritis and osteonecrosis are the major causes of premature hip-joint failure in young patients. Femoroacetabular impingement abnormalities are usually bilateral and are commonly associated with progression of the disease to the contralateral hip. Level of Evidence: Prognostic Level IV. See Instructions to Authors for a complete description of levels of evidence.