Children and young adults with hemolytic anemias requiring frequent transfusions develop increased liver iron content. We evaluated 15 chronically transfused children with sickle cell disease to determine whether spin-echo magnetic resonance (MR) imaging was useful in assessing the degree of iron overload. Quantitative MR parameters were correlated with liver biopsy iron determinations and serum ferritin levels. The best predictor of liver iron was the ratio of the intensities between the liver and paraspinal musculature on somewhat T1 weighted sequence (repetition time 0.5 s, echo time 28 ms), R2 = 0.58. Magnetic resonance was able to separate those patients with liver iron levels greater than 100 micrograms/mg (intensity ratios approximately 0.4), from those with levels less than 100 micrograms/mg (intensity ratios near 1). However, MR was unable to quantitate liver iron in patients with values ranging from 100 to 400 micrograms/mg since similar intensity ratios were present in this range. Thus, MR provides a qualitative rather than quantitative assessment of liver iron overload.