AbstractA new, special purpose, low-dose computed tomography scanner has been developed for the precise measurement of bone density in the distal radius. The instrument includes an125I source and four scintillation detectors which are scanned across a section of the forearm to produce a cross-sectional image. A number of innovative features have been included to improve patient comfort and scanner precision. The reproducibility for trabecular bone measurement was 0.5% for repeated scans in 22 subjects. The long-term precision in a group of normal subjects was better than 5 mg cm−3. The high precision and the separate measurement of trabecular bone make this technique suitable for the longitudinal study of bone density in metabolic bone disease.