Background: Acute esophageal mucosal lesions (AEMLs) cause circumferential mucosal damage in the lower esophagus in patients with deteriorating general health. However, its etiology remains unclear. AEML is often diagnosed and treated as severe reflux esophagitis (sRE), particularly that of Los Angeles classification grade D (sRE-D). This study aimed to determine whether it is appropriate to classify these two diseases according to the characteristics of the proximal mucosa of erosion as previously reported, and to clarify the clinical features of AEML in comparison with sRE-D.Methods: Patients were classified into AEML and sRE-D groups, based on previous reports. Patient background, presence of shock, medical history, medications, comorbidities, death during hospitalization, blood sampling data, endoscopic findings, and presence of stenosis after treatment were evaluated.Results: There were significantly more cases with comorbidities in the AEML group than in the sRE-D group, particularly comorbidities involving infectious diseases. In addition, abnormalities in blood test results were significantly more frequent in the AEML group than in the sRE-D group. This suggests that the onset of AEML may be due to peripheral circulatory disturbance caused by worsening general condition.Conclusions: AEML and sRE-D showed distinctly different features and it was considered reasonable to distinguish them. AEML, unlike sRE-D, may be caused by microcirculatory disturbances related to comorbidities rather than gastric acid reflux. However, it is under-recognized and should be considered in the setting of upper gastrointestinal bleeding in patients with deteriorating general condition.