The first 333 Charnley (Thackray, United Kingdom) total hip arthroplasties performed at the Mayo Clinic between 1969 and 1970 have been followed since that time. One hundred twelve patients (112 hips) remain alive at 20 years. Clinical results remain excellent. The Mayo clinical and roentgenographic hip scoring system rates the results as good to excellent in 39 of 69 hips (with all necessary data to calculate the entire score), fair in 13 hips, and poor in 17 hips. The clinical score alone showed satisfactory results in 77 of 112 hips. Some clinical deterioration was attributed to the advancing age of the patients (mean age at final follow-up evaluation, 84 years). Probable roentgenographic loosening (component migration, complete bone-cement interface, radiolucent line greater than 1 mm, cement fracture) was noted in 12 of 69 acetabular components (17%) and 28 of 69 femoral components (36%). Two patients had required revision since the last report at 15 years for a total of 38 patients (32 revised, 4 Girdlestone arthroplasties, 2 stem fractures not yet revised). The probability of surviving 20 years without revision of the components was 84% (83% for men, 85% for women). The rates of loosening, revision, and failure (revision, Girdlestone, or symptomatic loosening) remain linear over 20 years of follow-up evaluation. If the probability of revision is based on patient age at the time of the initial total hip arthroplasty, there is a significantly increased probability of revision in those patients less than 59 years of age (27%) compared to those 59-65 years of age (13%), 65-70 years (7.5%), and over 70 years (12%).