A synchronous tumor represents two histologically distinct neoplasms occurring at the same anatomic site, each displaying a distinct tumorigenesis pathway; they can be primary, secondary, or a mixture. The occurrence of an adenocarcinoma and lymphoma has been reported in gastrointestinal and pulmonary sites; however, such a finding in hepatobiliary system remains elusive. Primary hepatic lymphoma is rare, while primary biliary mucosa-associated lymphoid tissue lymphoma is an even rarer event; hence, its collision with an intrahepatic cholangiocarcinoma could be entirely missed both in practice and in the literature. We herein reported a case of biliary mucosa-associated lymphoid tissue lymphoma occurring synchronously with an intrahepatic cholangiocarcinoma in a 78-year-old female following a biopsy-proven intrahepatic cholangiocarcinoma and hepatectomy. Microscopic examination identified atypical lymphoid population intermingled with this intrahepatic cholangiocarcinoma. An immunohistochemical panel uncovered an incidental mucosa-associated lymphoid tissue lymphoma occurring with this intrahepatic cholangiocarcinoma. This clinically missed entity led to comprehensive systemic investigation/staging, with subsequent detection of bone marrow involvement by stage IV lymphoma. This unique case highlights the importance of astute histomorphological evaluation and thorough ancillary studies in identifying a clinically unsuspected neoplasm in close contact with a known tumor.