Nongastric primary extranodal mucosa-associated lymphoid tissue (MALT) lymphomas are uncommon, with around 0.1% occurring in the prostate. Even less frequent is the presence of MALT lymphoma synchronous with another type of neoplasm in the same organ, especially the prostate. Only a single case of concurrent adenocarcinoma and MALT lymphoma of the prostate has been reported in the literature. We report a rare case of primary extranodal marginal zone MALT lymphoma incidentally diagnosed during radical prostatectomy for an adenocarcinoma of the prostate in a 53-year-old patient. Fourteen months later a recurrence of the MALT lymphoma involving both sides of the diaphragm was found and was treated with chemoimmunotherapy. High-dose radiotherapy was delivered to residual bulky disease in the pelvic region. At 18 months from the end of radiation treatment the patient was without signs of relapse of MALT lymphoma. This preliminary result confirms that rare cases of MALT lymphoma of the prostate should be discussed and treated under the collaborative supervision of hematologists and medical and radiation oncologists. In fact, at an advanced stage of the disease, a chemotherapy regimen with additional consolidation radiotherapy could be an effective strategy, as in all other lymphomas.