Background: Since Sir John Charney in early 1960s began the orthopedic revolution in joint replacement surgery,a lot of modification and evolution has undergone in the development of suitable bearing surfaces which can withstand the higher demand of younger and more active patients.One of the most recent achievements in the field of bearing surfaces is the development of fourth generation large diameter femoral head ceramic on ceramic bearing surfaces.Advancement in bearing surfaces has expanded prosthetic head option from traditional sizes of 22,26,28,32 mm to diameter as large as 60mm.In our series 40 mm diameter ceramic femoral head was used with ceramic on ceramic bearing surfaces.Aim of our study is to observe the effect of large diameter ceramic femoral head with ceramic on ceramic bearing in primary total hip arthroplasty(THA).Material and Method: In the year between Jan 2010 to July 2012,total 68 hips were operated in our institution by using 40mm ceramic femoral head with ceramic on ceramic bearing surface,42male (46 hips) and 19female (22 hips) with mean age of 56 years(range 31-82 year).All the patients had scheduled follow-up at 2 months,6 months and one year.The patient s were evaluated by using x-ray,Harris Hip Score (HHS) and evaluating post-operative complications.Result: The average follow up was 18 months,range from 6-24 months.Preoperative HHS 51.7 which improved to 86.6 two month after the operation and to 96 to 100 at the final follow up (p<0.05).Out of 68 THA none of the hips were reported to have dislocation.One patient developed squeaking sound but was benign and occasional.None of the patient had to undergo revision or aseptic loosening.There were no cases of acetabular or femoral osteolysis till the end of follow up.Conclusion: Large diameter ceramic femoral head with ceramic on ceramic bearing surface not only significantly reduces the incidence of dislocation but also improves overall functional outcome.Long term studies will be required to determine the true efficacy of this new bearing surface