BACKGROUND: Negative lymph node (NLN) count has been reported to provide more accurate prognostic information than the N stage alone in patients with rectal cancer (RC). Since preoperative radiotherapy (Pre-RT) can significantly affect the LN status, it is unclear whether NLN count still has prognostic value count on survival of patients with RC who received Pre-RT. METHODS: In this study, clinicopathological characteristics, number of positive LNs and survival time were collected from Surveillance, Epidemiology, and End Results Program (SEER)-registered RC patients. Univariate and multivariate Cox proportional hazards models were used to assess the risk factors for survival. RESULTS: X-tile plots identified 9 (P < 0.001) as the optimal cutoff NLN value to divide the patients into high and low risk subsets in terms of cause specific survival (CSS). NLN count was validated as independently prognostic factor in univariate and multivariate analysis (P < 0.001). Subgroup analysis showed that NLN count was an independently prognostic factor for patients with stage ypII (P = 0.002) and ypIII (P < 0.001). CONCLUSIONS: Our results firmly demonstrated that NLN count provides accurate prognostic information for RC patients with Pre-RT.