Diffuse large B cell lymphoma (DLBCL) is classified as an aggressive lymphoma due to its poor prognosis regardless of the treatment. Almost all cases of DLBCL are treated using rituximab-combination chemotherapy, but spontaneous regression without any therapeutic modalities may rarely occur. A 35-year-old man complained of abdominal pain and discomfort. Positron emission tomography-computed tomography (PET-CT) demonstrated abnormal accumulation of fluorodeoxyglucose in the thickened wall of the small intestine and multiple lymphadenopathy. Laparoscopic lymph node biopsy was performed, and the diagnosis of DLBCL was made based on the biopsy findings. Soon after the laparoscopic biopsy, the patient felt free from any symptoms. Approximately three months later, no abnormal accumulation of fluorodeoxyglucose in the entire body was found on PET-CT. He has remained in complete metabolic remission for over three years according to PET-CT. We discuss the mechanism of this rare phenomenon.