The utility of magnetic resonance imaging (MRI) in the diagnosis of acute cholecystitis was evaluated in 72 consecutive individuals (5 healthy, 13 with chronic cholecystitis and silent gallbladder stones, 43 without biliary or diffuse liver disease, and 11 with acute cholecystitis and gallbladder stones) with a 0.5-T superconducting unit. On the T1-weighted (500/20) and less T1-weighted axial spin-echo images (620/25), the liver/gallbladder signal intensity ratio (mean +/- SD) was 2.5 +/- 0.51 (n = 5) and 1.8 +/- 0.29 (n = 8) in acute cholecystitis; 0.9 +/- 0.42 (n = 6) and 1.0 +/- 0.29 (n = 9) in chronic cholecystitis; and 0.9 +/- 0.14 (n = 5) and 0.8 +/- 0.19 (n = 43) in normal gallbladder, respectively. Our results indicate that the liver/gallbladder signal intensity ratio on the T1-weighted image may be a simple and reliable indicator for the diagnosis of acute cholecystitis; we suggest further investigation to confirm these results.