We reviewed 64 primary cementless porous-coated total hip arthroplasties using Omnifit Microstructured system (Osteonics, Allendale, New Jersey, U.S.A.). They were followed up for an average of 6 years (range, 5 years to 7 years and 11 months). The average Harris score was improved from 60.8 preoperatively to 86.2 postoperatively. The results were excellent in 3i cases(48.4%), good in 22 cases(34.4%), fair in 7 cases(I0.9%) and poor in 4 cases(6.3%). According to the last t'ollow-up radiologic findings, 61 cases(95.3%) were considered to he stable bony fixation and 3 cases(4.7%) to he stahle fibrous fixation. Neither unstahle fixation nor loosening of component was ohserved. But osteolysis was occured in 32 cases(50.0%) around prosthetic stem and in l6 cases(25.0%) around prosthetic cup. The mean linear wear of polyethylene insert was 1.46mm(range, 0.1 mm to 5.83mm). the linear wear rate was 0.23mm/year (range, 0.02mm/year to 0.81mm/year) and the excessive wear more than 2mm was ohserved in 15 cases. Reoperation was required in 18 cases(28. l%) after followup of 6 years (range, 4 years and 3 months to 7 years and 2 months); 11 had been reoperated and 7 were awaiting reoperation. The causes of reoperation were osteolysis and excessive polyethylene wear (more than 2mm) in 15 cases and osteolysis only in 3 cases. The result of primary cementless porous-coated total hip arthroplasties using Omnifit Microstructured system was acceptahle up to 5 years, but then increasing reoperation appeared to he due to polyethylene wear and osteolysis. Therefore, the routine follow-up of cementless porous-coated total hip arthroplasties is essential, especially after 5 years in order to detect and manage such prohlems early. And the modification in materials suhstituting metal-on-polyethylene articulation is required to reduce them.