Several studies have suggested that T cell-producing permeability factors might lead to proteinuria in minimal change nephrotic syndrome (MCNS). However, it is still unclear whether T-cell abnormalities cause MCNS. Immune dysregulation, polyendocrinopathy, enteropathy, X-linked (IPEX) syndrome is a rare disorder of the immune regulation system, which leads to severe autoimmune phenomena including autoimmune enteropathy, atopic dermatitis with high levels of serum immunoglobulin E (IgE), type 1 diabetes mellitus (T1DM), and severe infection such as sepsis, which frequently result in death within the first 2 years of life. This disease is caused by mutations in the FOXP3 gene that result in the defective development of regulatory T (Treg) cells. This report describes a 5-year-old boy with IPEX syndrome with a 3 bp deletion in the FOXP3 gene (c.748-750delAAG, p.250K.del) and a paucity of CD4(+) CD25(+) FOXP3(+) T cells. The boy's condition was complicated by MCNS in addition to many IPEX-related manifestations, such as atopic dermatitis, T1DM, enteropathy, sepsis and hemolytic anemia. This is the first report of IPEX syndrome complicated by MCNS, and our findings imply that Treg cell dysfunction may be crucial for the development of MCNS.