Reproducible animal models of Wilms tumor have been difficult to establish. We describe a model in which cells, banked from a patient with metastatic Wilms tumor, were implanted into nude mice, resulting in the development of primary renal and metastatic pulmonary lesions. Pathologically, the lesions resembled the blastemal component of anaplastic Wilms tumor. Primary tumors showed a significant propensity for growth in the kidney as opposed to other organs. Pulmonary metastases, histologically similar to the primary lesions, were regularly observed. This represents the first reproducible model of anaplastic, metastasizing human Wilms tumor. This system may prove effective for the study of factors influencing growth and angiogenesis in aggressive variants of Wilms tumor.