BACKGROUND: Allergic rhinitis (AR) is characterized by symptoms whose severity can be difficult to quantify due to the patient's subjective perception. The aim of this study was to compare two methods for assessing the severity of allergic rhinitis, a numerical score (SGS) and a visual analog scale (VAS), respectively. METHODS: A large study was carried out on more than 36,000 patients with a diagnosis of a non-complicated and non-treated seasonal allergic rhinitis (SAR) between May and August 2004 over all the metropolitan France. For each patient, a physician had to assess the severity of the AR calculating a score corresponding to the intensity of the symptoms as felt by the patient but also using an analog scale. RESULTS: SAR severity differed according to the used method: 18.94% of the patients were classed severe according to the SGS and 23.58% according to the VAS. Moreover, among the 35,126 people for which the two measures were available, 23.86% were classed severe according to one but not according to the other. These patients differ from those classed in the same manner by SGS and VAS in age, gender, type of doctor and geographical area. SGS and VAS correlated each other. Principal prescribed drugs for SAR were antihistamines and local steroids. CONCLUSION: Severity assessment varied according to the used method.