A 72-year-old man was admitted for examination of dyspnea and pitting edema of the lower legs in July, 1996. His hemoglobin level was 6.9 g/dl, and myelodysplastic syndrome (MDS) was revealed by bone marrow aspiration, and frequent transfusions were needed. His renal function rapidly deteriorated in the middle of August (BUN 45 mg/dl, Cr 4.8 mg/dl) and IgA nephropathy (IgAN) with marked intestinal nephritis was disclosed by renal biopsy. In November, joint manifestations of warmth and pain, which suggested arthritis, appeared at the bilateral wrist and ankle joints. Soon after receiving prednisolone (20 mg/day), the arthritis was relieved. Renal function also improved (BUN 41 mg/dl, Cr 21 mg/dl) and frequent transfusions were no longer necessary. This is a case with various clinical manifestations of MDS, IgAN, and arthritis, and appears to be the first MDS case complicated with IgAN. A number of case reports have identified immune abnormalities in patients with MDS. Immune and bone marrow abnormalities have been reported to be involved in the pathogenesis of IgAN. Thus, MDS could be complicated by IgAN. Their pathogenetic association is discussed in this paper.