Introduction. Adenocarcinoma is the most common prostatic malignancy where clinical management, Gleason score and recent updates in prostate cancer staging play critical role. Mantle cell lymphoma originates from malignant transformation of B lymphocyte in the outer edge of lymph node follicle, with pathognomonic overexpression of cyclin D1. We present a rare case of two neoplasms occurred in the same individual person. Case report. In a 68-year-old patient planned for radical prostatectomy during the hospital preoperative examinations using multislice computed tomography tumor mass confined to the prostate but also excessive lymph node enlargement were revealed. Tissue specimens were analyzed after using hematoxylin and eosin staining, as well as immunohistochemical biomarker panel. Having performed a thorough histological examination, a diagnosis of prostatic adenocarcinoma, Gleason score 3+4=7, ISUP GG2, was given. Microscopic analysis of lymph node involvement showed unexpected, diffuse proliferation of small lymphoid cells, with irregular nuclei, wide mantle zone and hyalinized blood vessels. After using immunohistochemical staining for specific markers, another diagnosis was set, and it was non Hodgkin mantle cell lymphoma. Conclusion. A prostatic adenocarcinoma can extremely rarely be in a coexistence with undiagnosed lymphoproliferative disease, such as non Hodgkin mantle cell lymphoma in our case.