Colonic diverticulosis is a condition which causes extensive bleeding of the lower gastrointestine in 40–50% of cases. In particular, right-sided diverticulosis, although uncommon requires lifesaving colectomy. Transfusion related acute lung injury (TRALI) is a transfusion reaction, which can occur after administration of various blood products. Although life threatening, it can be completely reversed usually within 72 to 96 hours. Here, we report a case of a young Caucasian male hospitalized due to severe anemia, hematochezia and extensive blood loss, all due to lower gastrointestinal hemorrhage from right-sided diverticulosis. These conditions were overlooked endoscopically and diagnosed then treated surgically with the right-sided hemicolectomy. During postoperative course, four hours after the last transfusion, patient developed fever, hypoxia and noncardiogenic pulmonary oedema, but made complete recovery through aggressive oxygen support within 96 hours. The aim of this case was to review current literature, to draw attention to a serious and under-diagnosed transfusion reaction, as well as discuss possible explanations for the diagnostic difficulties that occurred in this case.