A consecutive series of 31 patients with rheumatoid arthritis (RA) admitted over a 6-month period to the rheumatology unit of a District General Hospital were screened for possible osteomalacia. Transiliac bone biopsies were performed in 14 patients where the above diagnosis was suspected, yielding four (12.9%) cases of osteomalacia. All affected patients were elderly women who had a poor diet and were virtually housebound. Additional risk factors in two cases were partial gastrectomy and occult coeliac disease. Biochemical screening was of limited value in differential diagnosis, since elevated serum alkaline phosphatase levels were noted in both osteomalacic and non-osteomalacic patients. This study indicates that, in the West of Scotland at least, osteomalacia is a common, easily overlooked and treatable cause of morbidity in elderly patients with RA.