A 62-year-old Japanese man was referred to our hospital because of general fatigue. Abdominal ultrasonography and enhanced computed tomography scanning revealed many enlarged lymph nodes, mainly around the pancreas tail and the hilus of the spleen. Neither blood examination nor gallium scintigraphy revealed any abnormalities, whereas the diagnostic tuberculin test was strongly positive. Because we could not reach a final diagnosis, an exploratory laparotomy was performed. Histopathological examination revealed mantle-cell lymphoma. After chemotherapy combined with radiotherapy, the lymph-node swelling had disappeared. Herein, we report this case of stage-I mantle cell lymphoma that was difficult to differentiate from metastatic pancreatic cancer and abdominal tuberculous lymphadenitis.