Primary hepatic non-Hodgkin's lymphoma (NHL) is an extremely rare disease that is commonly neglected as a possible diagnosis. The present study reports the case of a middle-aged male with chronic hepatitis B in which primary hepatic NHL and rectal cancer occurred simultaneously. A large solitary tumor in the left lobe of the liver was incidentally detected on routine examination prior to the laparoscopic resection of the rectal cancer. Laparoscopic resection of the rectal cancer and a liver biopsy were performed simultaneously. The pathology revealed that the hepatic tumor was NHL and that the rectal cancer was adenocarcinoma. Systemic staging revealed no evidence of nodal or bone marrow involvement, therefore, primary hepatic lymphoma (PHL) was diagnosed. PHL associated with rectal adenocarcinoma is extremely rare and to the best of our knowledge, has never been reported. At present, the cause and most effective therapy for the condition remain unclear.