Patients who present with hip arthrodesis can have a history of surgical hip fusion (e.g., infection treatment) or spontaneous fusion (e.g., rheumatoid, ankylosing spondylitis). Takedown of the arthrodesis with subsequent conversion to total hip arthroplasty (THA) may resolve debilitating pain or functional deficits in these patients. Takedown and conversion may be performed as a single procedure or as a staged procedure. This is a technically challenging procedure, and complication rates are higher than primary THA. The goal of this operation is to restore hip mobility to relieve pain on the hip and adjacent joints. Some patients may have a persistent limp or lurching gait. This chapter outlines the basic principles in treating the painful hip arthrodesis and highlights two case reports (one simultaneous, one staged) of arthrodesis takedown with conversion to THA.