We sought to estimate the prevalence of reduced bone mass, defined by lumbar spine bone mineral density (LS-BMD) (z-score < −2.0), and to determine the factors associated with LS-BMD after liver transplantation in children and adolescents. LS-BMD z-scores were measured in a sample of subjects who had undergone liver transplantation in childhood or adolescence using dual energy x-ray absorptiometry (DXA). One hundred nine patients underwent DXA. The mean age at transplantation was 4.3 years (median, 1.8 years), and mean duration since transplantation was 6.2 years (median, 5.8 years). The mean weight z-score was −0.130 (SD, 1.26). The mean LS-BMD z-score was −0.243 (SD, 1.27). Eight patients, or 7.3% (95% confidence interval [CI], 2.4% to 12.2%), had reduced bone mass. Compared with those without reduced bone mass, subjects with reduced bone mass were more likely to have been treated for rejection at least once (87.5% versus 51.5%; P = .07), and had greater cumulative exposure to prednisone during the year before DXA (92.3 versus 26.2 mg/kg/y; P = .001). Multiple linear regression determined that LS-BMD z-score was positively associated with time since transplantation and weight z-score and negatively associated with cumulative prednisone exposure. Serum 25-OH vitamin D was measured and reduced (< 15 ng/mL) in 5 of 87 patients, one of whom had reduced bone mass. In conclusion, the prevalence of reduced bone mass was 7.3% in our population. Only certain patients appear to be at risk for low BMD, including those with a history of rejection. Screening for reduced bone mass may be appropriate for these patients.