A 48-year-old man was admitted to our hospital with continuous abdominal pain. Computed tomography showed free air in the abdomen, and the patient was diagnosed with pan-peritonitis due to perforation of the stomach or small intestine. We performed an emergency operation, during which we found a perforation, 15cm from the ligament of Treitz; therefore, we performed partial jejunal resection. We found one deep ulcer and one ulcer with perforation in the resected specimen. Pathological findings showed a primary well-differentiated adenocarcinoma in each ulcer. The patient has a familial history of cancer and a history of rectal cancer; therefore, we suspected Lynch syndrome. Accordingly, we performed the microsatellite instability (MSI) test and high MSI was detected. Primary jejunal and ileal cancer usually occurs with obstruction or hemorrhage; however in Japan, there have been only 13 cases of jejunal and ileal cancer with perforation. Herein, we report a case of adenocarcinoma of the jejunum with perforation, along with a literature review.