The authors studied the long-term fatty replacement of bone marrow in 23 patients who had received radiation therapy for Hodgkin disease, with T1-weighted magnetic resonance imaging and quantitative chemical shift imaging. T1-weighted images revealed a mostly homogeneous high-signal-intensity pattern, in contrast to the hypointense pattern of nonirradiated marrow. The degree of fatty replacement was objectively assessed with chemical shift imaging, comparing patients to age-matched healthy volunteers. The authors found an increase in relative fat signal of 37% in the thoracic spine and 34% in the lumbar spine. The relative fat signal of nonirradiated pelvic and femoral marrow was decreased by 8%, indicating marrow reconversion. No radiation dose dependence was found in the range from 25 to 50 Gy. No signs of marrow regeneration were observed 15-126 months after radiation therapy. With chemical shift imaging, the degree of long-term radiogenic fatty replacement of the bone marrow can be quantified, confirming the lack of regeneration after radiation therapy for Hodgkin disease.