Chronic infection of a seminal vesicle cyst is an extremely rare disorder worldwide. To date, only two cases, which were diagnosed initially by the use of contrast-enhanced CT or non-enhanced MR imaging, have been reported in the literature. We report here a case of a 78-year-old man with chronic infection of a seminal vesicle cyst to illustrate the usefulness of the pelvic contrast-enhanced MRI in making a definitive diagnosis of the rare disorder. In addition, a brief review of the relevant literature is presented.