1. A study is reported of 190 femora in 174 patients in whom self-curing acrylic cement had been present in the medullary cavity of the upper end of the femur for the fixation of an endoprosthesis for an average period of four years.

2. The bone remained radiologically normal in 81 per cent of cases.

3. Improvement in the thickness of the cortex from pre-existing atrophy was noted in 2·6 per cent.

4. In 4·7 per cent the bone showed some atrophy after insertion of the cement. This exceeded 10 per cent in only two cases. All were originally osteoporotic from polyarthritis; all were satisfactory as regards the arthroplasty itself, and the atrophy could usually be explained by disuse resulting from the state of the opposite lower extremity, or the knee on the same side.

5. In 9·4 per cent there was fusiform hypertrophy of the femoral cortex, the bony texture remaining normal. This appearance was considered physiological and benign.

6. In 2·2 per cent there were changes for which the most likely explanation is chronic non-suppurative osteitis, though no collateral evidence of infection was found.

7. In 44·8 per cent there was a thin line of condensation in the cancellous bone demarcating the outer limits of the cement. This is considered to be physiological and not to indicate failure of immobilisation.

8. In 37·2 per cent there was slight resorption of the cut surface of the calcar femorale. This is considered to be physiological and to confirm the efficacy of weight transmission by cement lower down in the medullary cavity.