A 73-year-old man suffering from supra-pubic pain, dysuria and urinary retention for 3 months was slightly hypertensive, normoglycaemic, with normal renal biochemical parameters. In digital rectal examination prostate was slightly enlarged, but a cystic mass was palpable arising from the upper boarder of the prostate. He was examined by pelvic magnetic resonance imaging (MRI) with a preliminary diagnosis of pelvic mass or abscess. MRI examination revealed a homogeneous, well demarcated giant cystic mass (arrows) 12 x 8 x 6 cm in size at the posterior of the urinary bladder and superior of the prostate and seminal vesicles (A). The cyst was displacing the rectum, prostate and the urinary bladder. The cystic mass content was slightly hyperintense on T1-weighted images (C) and significantly hyperintense on T2-weighted images when compared to muscle tissue (B). The cyst was associated with seminal vesicles and MR signal features of the cyst content were similar with right seminal vesicle (C). The left seminal vesicle content was hypointense on T1- and hyperintense on T2-weighted images (Fig. B, C).