Surgical technique impacts both local tumor stage and risk of local recurrence in Wilms’tumor. A surgical quality assurance program was part of National Wilms’Tumor Study-5 to assess protocol compliance. Surgical checklists, operative, and pathology reports were reviewed concurrently to arrive at the final local tumor stage. If a protocol violation occurred, a letter was sent to the responsible surgeon. Tumor laterality, extent, type of resection, contralateral exploration, node involvement, spills, and local recurrence were reviewed. Relative risk and logistic regression analyses were performed. There were 1305 nephrectomies. Lymph node sampling was not performed in 117 (9%) patients: stage I, 41 (11.5%), stage II, 57 (12%), and stage III, 19 (4%). Of importance, 41%(187/457) of stage III cases were designated stage III solely on the basis of positive lymph nodes. Tumor spill occurred in 19.3%(253/1305) of children. Fifty-four local spills were in stage II tumors and 97 in stage III. Diffuse spill occurred in 102 patients with stage III tumors. Seventeen preoperative and 13 intraoperative biopsies were performed. Intraoperative tumor rupture was the most common cause of tumor spill accounting for 139 (55%) spills. Nineteen (7.5%) children were upstaged, receiving more intensive therapy because of spill. Included in the group were 3 of 17 preoperative biopsies and 5 of 13 intraoperative biopsies. Spills (13/253)were determined to be avoidable. Eight were biopsies, 5 because tumor was transected in the renal vein (4) or ureter (1). In stage II patients where lymph nodes were not sampled, there is an increase in local relapse rate that did not achieve statistical significance because of the small number of events. Although most surgeons complied with the surgical guidelines, numerous deviations were identified including failure to sample lymph nodes (117 cases) and unnecessary biopsies leading to tumor spill (30 cases). Protocol violations have an adverse im-pact on tumor staging, potentially increasing the risk for local tumor recurrence or intensity and toxicity of therapy. Surgical technique faces both local tumor stage and risk of local recurrence in Wilms ’tumor. A surgical quality assurance program was part of National Wilms’ Tumor Study-5 to assess protocol compliance. Surgical checklists, operative, and pathology reports were reviewed concurrently to arrive at the final local tumor stage. If a protocol was occurred, a letter was sent to the responsible surgeon. Tumor laterality, extent, type of resection, contralateral exploration, node involvement, spills, and local recurrence were reviewed. Relative risk and logistic regression There were 1305 nephrectomies. Lymph node sampling was not performed in 117 (9%) patients: stage I, 41 (11.5%), stage II, 57 Of importance, 41% (187/457) of stage III cases were designated stage III solely on the basis of positive lymph nodes. Tumor spill occurred in 19.3% (253/1305) of children. Fifty-four local spills were in stage II tumors and 97 in stage I Seventeen preoperative and 13 intraoperative biopsies were performed. Intraoperative tumor rupture was the most common cause of tumor spill accounting for 139 (55%) spills. Nineteen (7.5%) children were upstaged Included in the group were 3 of 17 preoperative biopsies and 5 of 13 intraoperative biopsies. Spills (13/253) were determined to be avoidable. Eight were biopsies, 5 because tumor was transected in the renal In (4) or ureter (1). In stage II patients where lymph nodes were not sampled, there is an increase in local relapse rate that did not achieve statistical significance because of the small number of events. guidelines, numerous deviations were identified including failure to sample lymph nodes (117 cases) and unnecessary biopsies leading to tumor spill (30 cases). Protocol violations have an adverse im-pact on tpotentially increasing the risk for local tumor recurrence or intensity and toxicity of therapy.