Three hundred forty-three primary hip arthroplasties performed prior to June 1984 were followed for two years, and an additional 204 were followed for five years. Anteroposterior and lateral roentgenograms taken at annual intervals were used for comparison. At two years, 78% of the hips showed roentgenographic signs of stem osseointegration. Seventeen percent were clinically stable but demonstrated reactive lines surrounding the porous surface, indicating lack of bone-ingrowth fixation. Four percent showed late implant migration. Using late migration as an end point, a survivorship analysis of the stem stability was performed. The cumulative survival rate for stable fixation was 94% at five years and 88% at eight years. Among the 143 undersized stems, 17 showed late migration and two failed by stem fracture at six and eight years, giving a cumulative survival rate of 77% at eight years. By contrast, there were no roentgenographic failures among 200 canal-filling stems. Three stems were revised: two for stem fracture and one for loosening with infection. Proximal stress shielding occurred only in bone-ingrowth stems and was slightly progressive. Unstable implants produced progressive intramedullary canal widening. The clinical results were superior when the roentgenograms showed signs of bone-ingrowth fixation. Functional recovery in such cases was equivalent to that for cemented arthroplasty.