Background: Previous epidemiologic studies have reported that a history of allergy is associated with reduced risk of colorectal cancer and other malignancies. However, no information is available for the association between allergy and the risk of lymph node metastasis. Our study was designed to determine this association in rectal cancer. Methods: Patients who were treated at our hospital in the period from January 2003 to June 2011, and with a pathologically hospital discharge diagnosis of rectal adencarcinoma, were included. The clinical, laboratory, and pathologic parameters were analyzed. A multivariate logistic regression model was used to determine the association. Moreover, for type of allergic drug, sub-group analysis was performed. Results: 469 patients were included, including 231 with pathological lymph node metastasis (pLNM) (49.3%) and 238 without pLNM. Univariate analysis showed, compared with patients without pLNM, patients with pLNM had a younger age (60.6 +/- 12.8 yr vs. 63.6 +/- 12.2 yr, P = 0.012), a lower percentage of drug allergy (8.7% vs. 16.0%, P = 0.016), an increased CEA (median/interquartile-range 5.40/2.40-13.95 vs. 3.50/2.08-8.67, P = 0.009), and a lower serum sodium (141 +/- 3.1 mmol/L vs. 142 +/- 2.9 mmol/L, P = 0.028). Multivariate analysis showed that drug allergy was associated with a reduced risk of pLNM (OR = 0.553; 95% CI, 0.308-0.994; P = 0.048). In addition, our results showed that: (1) for tumor classification, patients with drug allergy had a higher percentage of group patients with pT1/pT2; and (2) for type of allergic drug, this inverse association was found for penicillins, not for other allergic drugs. Conclusion: Drug allergy is associated with a reduced risk of pLNM in rectal cancer.