A prospective, randomized, double-blind, multicenter trial was done to determine if the addition of hydroxyapatite and tricalcium phosphate to the porous coating of a cementless femoral component would result in improved clinical and radiographic outcomes. Patients were randomized to receive identical porous-coated stems with (n = 159 hips) or without (n = 159 hips) hydroxyapatite and tricalcium phosphate coating. At 2 to 5 years followup (mean, 37 months), no implants were revised for aseptic loosening. There was no difference in clinical function between the two groups with respect to the Harris hip score or Western Ontario and McMaster Universities Osteoarthritis Index scores. Bony ingrowth occurred frequently in both groups with 99% of the hydroxyapatite and tricalcium phosphate group and 98% of the control group showing radiographic evidence of osseointegration. Implants coated with hydroxyapatite and tricalcium phosphate had significantly fewer radiolucencies adjacent to the porous coating, indicative of improved osseointegration. Radiolucencies were present in Gruen Zones 1, 7, 8, or 14 in 25% of the control group and in 7% of the hydroxyapatite and tricalcium phosphate group. This improved osseointegration could serve as an added barrier to particulate debris migration and increase the long-term survivorship of the implant.