A 53-year-old Japanese male was diagnosed with atopic dermatitis and initiated treatment with a local dermatologist in February 2001. A routine medical check-up revealed proteinuria, microscopic hematuria and slight elevation of serum creatinine level in spring 2006. He was referred to our hospital for nephrology consultation and followup.In December 2009, he developed a sudden high fever of greater than 39 °C with sore throat. In addition, his serum creatinine level greatly increased to 4.6 mg/dl. His prevalent renal illness was thought to be rapidly progressive glomerulonephritis (RPGN). Soon after admission, kidney and skin biopsies were performed. The kidney specimens showed that the glomeruli had proliferative mesangial cells strongly positive for anti-IgA antibody, 75% of which manifested fibrocellular crescentic formation surrounding the Bowman's capsules. His skin disease was pathologically proven to be mycosis fungoides(MF). It is likely that his kidney disease was exacerbated by the upper respiratory tract infection and converted to RPGN. Ash is kidney function rapidly declined, hemodialysis therapy was initiated and he remains on chronic dialysis therapy. This is a serious case of IgA nephropathy associated with MF,which developed into RPGN and subsequent end-stage renal disease.