The qualitative and quantitative MRI findings in 16 patients with focal nodular hyperplasia (FNH) of the liver are described; nine of these were confirmed histologically. A central scar is typical of FNH and provides a reliable diagnosis. This finding was seen in half the cases. If the scar is not demonstrable, the following features suggest the diagnosis: smooth margins, homogeneous signal distribution, increased signal intensity in T2-weighted spin-echo images and reduced signal intensity in inversion-recovery sequences. The T1 and T2 relaxation times in FNH are increased by about 30% compared with normal liver tissue.