Leprosy can cause acute reactions, which may be type 1 (reverse reaction) or type 2 (erythema nodosum leprosum - ENL). ENL has been classified as mild, moderate, or severe. In order to standardize the classification, the Erythema Nodosum Leprosum International Study (ENLIST) Group has developed an objective scale, the ENLIST ENL Severity Scale (EESS), which was the first validated severity scale of ENL in the world. The goal of the study was to describe the sociodemographic and clinical characteristics of patients with ENL attending a tertiary hospital in Piauí, Brazil, classifying them according to the EESS.A descriptive cross-sectional observational study was conducted on 26 patients recruited sequentially from May 2017 to February 2018. Their data were statistically analyzed and compared against each other through a structured questionnaire.According to the score obtained in the scale, the patients were divided into two groups: mild ENL and moderate/severe ENL. The extent and number of nodules were related to the severity of the cases, and these data were statistically significant. The majority of the patients were male, between the ages of 31 and 49 years old, with low educational level, and residents in the urban area.This was the first study to use EESS in Brazil. This scale is easy to apply and allows for the enhancement of treatment protocols. The study also showed a correlation between the number and extension of nodules and the severity of the condition.