We report on a 6-month-old child presenting with chronic diarrhea, failure to thrive, eczema, autoimmune hemolytic anemia (AIHA), insulin-dependent diabetes mellitus (IDDM), hypoalbuminemia, and proteinuria. Renal biopsy showed membranous glomerulonephritis. A diagnosis of Immunodysregulation, polyendocrinopathy, enteropathy, x-linked (IPEX) syndrome was subsequently confirmed by DNA analysis, which demonstrated the presence of a mutation in exon 2 of the FOXP3 gene (303–304 del TT). Proteinuria secondary to membranous glomerulonephritis is a novel feature of IPEX syndrome. Membranous glomerulonephritis went into remission after the patient had received hematopoietic stem cell transplantation (HSCT).