Wilms' tumor, the hyponatremic/hypertension syndrome, and an elevated atrial natriuretic factor.

Hyponatremia and malignant hypertension are rare manifestations of Wilms' tumor. Hyponatremia associated with malignant hypertension of any cause is not explained. We present a patient with hyponatremia, malignant hypertension, Wilms' tumor, and an elevated atrial natriuretic factor (ANF). We believe the elevated ANF caused the hyponatremia.