We describe a 23-year-old white man who presented with anasarca and a new periumbilical mass. He had preserved kidney function and laboratory findings consistent with nephrotic syndrome, including 9.7 g/day albuminuria. Serum serologies were positive for anti-SSa and anti-SSb and low complements but were negative for antinuclear antibody. Pathologic findings of the abdominal mass showed a mammary-type myofibroblastoma. A kidney biopsy revealed a diffuse proliferative and membranous immune-mediated glomerulonephritis with 10% interstitial fibrosis. This is a novel case of mammary-type myofibroblastoma associated with nephrotic syndrome mimicking a proliferative lupus pattern.