Present therapy in Wilms tumor is based upon prognosis. Current trends suggest less intensive chemotherapy and/or radiation therapy for children with favorable histological disease who are considered at low risk for recurrence and increasing the amount of therapy for those with unfavorable histological tumors who are at high risk for recurrence. Currently, pathological stage and histological appearance are used to predict prognosis. We tested a new approach. Histological sections of surgical specimens were obtained from 9 children treated for unilateral Wilms tumor. All patients had favorable histological disease, and received postoperative chemotherapy and/or radiotherapy. These specimens were evaluated by nuclear morphometry with the Hopkins Morphometry System to determine if nuclear shape descriptors could distinguish children who responded to therapy from those whose tumor recurred. Nuclear roundness, ellipticity, convexity and bending energy accurately separated the groups. Nuclear morphometry may provide useful information that will aid in predicting which children with Wilms tumor will respond to therapy and warrants further investigations.