The trabecular bone density and bone marrow fat content in eight patients with type 1 Gaucher disease were measured with the use of a modification of dual-energy computed tomography (CT). The results were compared with those in published reports of single-energy quantitative CT measurements in healthy subjects and with dual-energy data obtained in studies of healthy premenopausal women and elderly osteopenic women. The trabecular bone mass was moderately decreased in patients with Gaucher disease. The bone marrow fat content was markedly diminished, presumably due to replacement of marrow fat by Gaucher cells. In healthy and osteopenic subjects single-energy quantitative CT values were lowered by the presence of marrow fat. Comparable single-energy measurements in patients with Gaucher disease reflect greater degrees of bone loss. Low levels of marrow fat may prove to be a valuable marker of the severity of marrow disease.