BACKGROUND Multiple primary malignancies in a single patient are considered to be quite rare. However, due to the wider availability of advanced imaging methods and, more regular check-ups, they are becoming more common in clinical practice. To determine the diagnosis of multiple primary malignancies, each tumor must be completely separate and cannot be from metastasis of one or the other. Coexisting hepatocellular carcinoma and gallbladder carcinoma are extremely rare, with only a few case reports published. We believe that to determine the most effective therapeutic management, the results of as many cases as possible should be documented. Regardless of limited data, curative resection may be the most beneficial treatment option in terms of overall survival. CASE REPORT We present the case of a 64-year-old man first diagnosed with hepatocellular carcinoma with possible infiltration of the gallbladder wall as appeared on a CT scan. However, the definitive histopathologic examination revealed the coexistence of hepatocellular carcinoma and gallbladder carcinoma. In this case report, we offer an insight into the entire diagnostic process, as well as the chosen surgical approach and adjuvant therapy. Moreover, we present our approach to preoperative biopsy, the decision-making process throughout the whole diagnostic and therapeutic course, and the achieved results. CONCLUSIONS In cases of double primary malignancies, the choice of therapeutic strategy depends on the type and stage of both malignancies, but procedures with curative intent are superior. We present the outcome and overall survival of the patient after the surgery and adjuvant chemotherapy for synchronous hepatocellular carcinoma and gallbladder carcinoma. Since the liver is the organ most commonly affected by metastatic dissemination of primary tumors, exclusion of metastatic disease is particularly important.