Small cell carcinomas are well-recognized tumors known to occur predominantly in the lung. These neoplasms are occasionally associated with a variety of paraneoplastic syndromes. Four cases of paraneoplastic glomerulopathy associated with small cell lung carcinoma have been reported. However, there have been no reports in the literature indicating an association between endometrial small cell carcinoma and paraneoplastic glomerulopathy. We report a case of neuroendocrine small cell carcinoma of the endometrium associated with membranous glomerulonephritis (MGN), which appeared to be a component of an unusual paraneoplastic syndrome. A 33-year-old multiparous woman presented with abnormal vaginal bleeding and abdominal bloating. Endometrial biopsy revealed neuroendocrine small-cell carcinoma of the endometrium. On the eighth day of hospitalization the patient suddenly developed renal failure. Renal biopsy revealed MGN, probably due to tumor-antigen-related immune complex deposition. Small cell carcinoma of the endometrium may be associated with paraneoplastic MGN. Medical staff should take into account the possibility of a preexisting glomerular injury when managing a patient with small cell carcinoma of the endometrium.