Considering that the incidence of colorectal (CRC) and prostatic cancer (PC) increases with age, metachronous and synchronous tumors can often affect the same patient. Despite the importance of this subject for the diagnosis and management of oncologic patients, in medical literature the data are scarce. The aim of the study was to evaluate the incidence and the characteristics of double/multiple primary malignant tumors (D/MPMTs) with colorectal and prostatic origin, in patients admitted to a reference hospital in West Romania. A 4-year retrospective observational study (2016–2019) was conducted by analyzing the medical records of all patients admitted in the hospital. Demographic and clinical data, as well as tumor-related parameters, were extracted. We identified 413 consecutive hospitalized patients with PC, and 21 (5%) of them also had a primary CRC. At the time of diagnosis, the mean age of the patients with PC was 71.2 ± 6 years, and 71.8 ± 10 years for patients with CRC. Synchronous PC and CRC tumors were identified in 3/21 cases and metachronous tumors in 18/21 cases. Prostate cancer was the first tumor to be diagnosed in 13/18 cases and CRC in 5/18 cases. The most frequent subtype of PC was acinar adenocarcinoma (90%) and for CRC cases, conventional adenocarcinoma (90%). Prostate and colorectal cancers tend to co-occur in a single patient. The diagnosis of one of these two types of tumors should imply the screening for the other one, because these patients require a multidisciplinary and personalized approach.