The authors describe an unusual case of acute renal failure in a 50-year-old woman with a history of breast carcinoma. The breast carcinoma was treated with 4 cycles of chemotherapy. After chemotherapy, she felt fatigued and noticed decreased urine output. Her serum creatinine level had risen from 0.8 to 10.1 mg/dL (71 to 893 micromol/L). Renal biopsy was done that showed a severe crescentic glomerulonephritis secondary to dense deposit disease. This case is extremely unusual in that: (1) Dense deposit disease developed in a 50-year-old woman, whereas it is primarily a disease of children and young adults, and (2) the patient was being treated with immunosuppressive chemotherapy for breast carcinoma when dense deposit disease developed, thus posing a therapeutic dilemma.