Femoral　prosthesis　before　total　hip　arthroplasty　(THA)　predicted　by　Proximal　Femoral　CT　scanning.　Prior　to　THA,　61　hip　bones　in　52　cases　were　scanned　by　CT　to　measure　the　minimum　inner　diameter　of　cavum　medullare　in　femur　isthmus.　The　corresponding　type　of　femoral　prosthesis　was　selected　according　to　the　size　of　the　cavum　medullares.　The　conventional　template　measuring　method　was　used　as　a　contrast.　The　minimum　inner　diameter　of　cavum　medullare　in　femur　isthmus　and　the　medial　diameter　of　cavum　medullare　of　resected　femur　had　strong　correlation　with　the　type　of　femoral　prosthesis　(r　=　0.97-0.99,　P　＜　0.05).　In　terms　of　pre-operative　femoral　prosthesis　selection,　the　CT-based　isthmus-measuring　method　had　an　excellence　rate　of　47.5%.　This　method　had　an　excellence　rate　of　52.5%.　The　CT-based　resected-femur-measuring　method　had　better　accuracy　in　pre-operative　femoral　prosthesis　selection　for　the　patients.　©　2012　Springer-Verlag.