Prostatic ductal adenocarcinoma (PDA) is an uncommon histological variant of prostatic adenocarcinoma that may present clinically as a cystic mass [1-3]. We report a case of cystic PDA presenting as a cystic perirectal mass in a 61 year old male. Fine needle aspiration cytology showed malignant cells with round-oval to focally elongated nuclei, conspicuous nucleoli, and amphophilic cytoplasm with focal acinar formation. Tumor cells were positive for prostate-specific antigen; however, the cytology was non-specific for site of origin. The radical cystoprostatectomy specimen revealed the true site of origin and showed a cystic PDA adjacent to conventional prostatic acinar adenocarcinoma. Our objective is to describe the common cytological features of PDA and to analyze the differential diagnoses associated with cystic masses of the prostate.