Purpose Our study aimed to help establish the standard of the minimum number of lymph nodes examined for rectal cancer,by estimating the probability that a pathologically node-negative patients has,indeed,free of positive nodes.Experiment Design 31,853 eligible patients with stage Ⅰ-Ⅲ adenocarcinoma of the rectum between 2004 and 2013 were identified from the Surveillance,Epidemiology and End Results(SEER)database.Patients were categorized into two groups: those treated with surgery directly(SURG)and those treated with neoadjuvant therapy(NEO).Nodal staging score(NSS)was developed based on pT/ypT stage and the number of nodes examined by using a beta-binomial model.Results In both cohorts,the probability of missing a positive node was estimated to approximately 16%if 12 are examined,but drops to around 10%when 20 nodes are examined.In SURG cohort,to rule out 90%possibility of false staging,three,seven,28,and 32 lymph nodes would need to be examined for patients with pT1-4 disease,respectively.While in NEO cohort,four,seven,12,and 16 lymph nodes would need to be examined for patients with ypT1-4 disease to guarantee an NSS of 90%.Conclusions Our study developed a model to estimate of false node-negative rate as a function of pathological tumor stage and number of lymph nodes examined.By determining whether a node-negative rectal cancer patient is adequately staged,NSS may serve as an instrument to assist in tailoring postoperative management and surveillance for patient with rectal cancer.