In Denmark (5.3 mill. inhabitants), a national register for total hip replacements was established in January 1995. During the first 4 years, 18,222 primary total hip replacements (THR), 3,343 revisions and 6,071 follow-up examinations have been registered. During the same period, the incidence of primary THR per 100,000 inhabitants has increased from 72 in 1995 to 93 in 1998. The mean age at the primary replacement was 68 years, 59% were women and in 75% primary arthrosis was the diagnosis. An increasing use of uncemented implants has been observed both in primary THR and in revision. 64% of the primary THR were cemented and in revisions of both components, 49% were cemented. The reasons for revision were aseptic loosening in 63% of the cases followed by dislocation in 12% and deep infection in 11%. When assessed by the Harris Hip Score, primary THR and revisions resulted in a considerable improvement in pain and function, with the best results after primary operation. After 3 years, the prosthesis survival of all primary THR was approximately 97%. The lowest survival was observed in younger men with a hybrid prosthesis, usually uncemented cup and cemented stem.