Aim: The HA coated Osteonics-Omniþt hip endoprosthesis with the PSL (peripheral self locking) acetabular cup was implanted in our institution between the years 1992 to 1996. This cup is spheric with several holes for screw þxation, and a Òwafße-likeÒ macrostructure along the periphery of the component. This component was connected with the HA coated Osteonics stem. Material and methods: A total of 173 patients (178 hips) mostly < 65 years old (average age, 50.5 years; range, 17–70 years) received a proximally HA-coated femoral prosthesis with a hemispheric metal-backed, HA-coated acetabular cup (PSL), with an average follow-up of 7,5 years (range 5 to 9 years). All operations were performed in the University Hospital by senior surgeons. There were 80 male and 86 female patients. The indications for operation were primary arthrosis in 84, secondary arthrosis (AVN, LPC etc.) in 34, rheumatoid arthritis in 34, posttraumatic in 13, and tumor in one case. This material compiles those cases revised for loosening of the acetabular cup (PSL). Results: Twenty-nine acetabular components have been revised due to the loosening and/or periacetabular osteolysis or access wear of the liner. Add to this there are 6 patients/hips on the waiting list. The total number of loose acetabular cups is therefore 35 (20%). The radiological signs of loosening have usually been evident with clear radiolucent lines (RLL) starting from the Gruen zone 3. At operation the cup have been loose with no signs of bony ingrowth and the HA coating resorbed away in most of the cases. There were no breakage of the screws. Survivorship analysis, based on those cases reported into the Finnish Arthroplasty Register, predicted a survival rate of 88.5% at four years (95%Cl 83.8–93.3, 93 at risk). Conclusions: The loosening rate of more than 20% with only 88.5% survivorship at four years is not acceptable. The bad results are mainly connected with the loosening of the PSL (peripherial self locking) type of acetabular component. The main features of that component are no porous coating, and the HA on the smooth surface. According to the literature and other Nordic implant registers the results with this kind of concept have been alarming. Theoretical disadvantages to HA coatings include the critical parameters required for its application on surfaces, and retrieval studies of implants at the time of revision indicate the potential concern for dissolution and delamination of the coating, especially on smooth metal surfaces. Also the manufacturer have changed the concept towards Ha on porocoating (Securþt). The clinical trials so far have focused on the performance of the femoral component the acetabular components have been of varying designs without any þrm conclusions. The results of this study do not indicate any signiþcant clinical advantage to the use of HA coated acetabular components in primary total hip arthroplasty.