MRI findings in three cases of pseudomyxoma peritonei, in two cases associated with visceral invasion, are described. MR imaging using the same morphologic criteria as described in ultrasonography and CT suggested the diagnosis in all three cases. In T 1 weighted images (SE 400/28 ms) the hypointensity of signals of both implants and mucoid ascites was found to approach that of muscle tissue. In T 2 weighted images (SE 1600/40, 80, 120 ms), however, there was general hyperintensity of signals, which was more pronounced in mucoid ascites than in implants, and which approached signal intensities of water. Invasion of the viscera was very well depicted in all cases.