Granulomatous prostatitis (GP) is an unusual and benign inflammatory condition of the prostate, where autoimmunity has been recognized as a key factor in the pathogenesis of GP in a subset of patients. Clinically, GP poses diagnostic challenges as it may strongly mimic prostate cancer from a clinical, biochemical and radiological point of view. The occurrence of GP in patients suffering from psoriasis, a systemic autoimmune disease, has never been investigated. We describe the case of GP in a patient with psoriatic arthritis presenting with an increased prostate specific antigen level, and evidence of a nodular lesion visualized by prostate multiparametric magnetic resonance imaging, which was highly suspicious for aggressive prostate cancer.