Similar methods for measuring bone density using quantitative computed tomography have been proposed by Cann and Genant and by Firooznia et al. This study was done to evaluate the long-term reproducibility of quantitative computed tomography in the clinical setting. An anthropomorphic phantom was evaluated over an 18-month interval. A variation of +/- 2.2% was obtained, substantiating that quantitative computed tomography can be done in a reproducible manner over an extended time interval.