The efficacy of primary cementless acetabular reconstruction in patients younger than 50 years of age was analyzed in 79 consecutive cementless, hemispheric, porous coated acetabular reconstructions (Harris-Galante-I). The average age was 37 years at surgery (range, 20-49 years). The average followup was 106 months (range, 78-126 months). No acetabular reconstructions were revised for aseptic loosening. Two stable acetabular reconstructions were revised during femoral revision. Two excessively worn polyethylene liners were exchanged and one acetabular osteolytic area was debrided and grafted; these procedures retained the metal shell. At final followup, all 72 acetabular reconstructions were radiographically stable. Acetabular osteolysis occurred in five cases (7.4%), from 84 to 104 months. Acetabular or femoral osteolysis occurred in patients with increased polyethylene wear. Polyethylene wear was inversely related to the patient's age. Using revision and loosening, the Kaplan-Meier 10 year survival of the acetabular reconstruction was 98.8% (95% confidence interval, 96.6%-100.%). The intermediate results of cementless, hemispheric, porous coated acetabular reconstruction in younger patients was excellent with no radiographic loosening. At 7- to 11-year followup, osteolysis was the most common problem and increased in frequency and extent with continued in vivo duration.