We have evaluated 160 patients diagnosed of erythema nodosum (EN) on the basis of clinical and/or histopathological criteria to assess their etiology and their major epidemiological, clinical and laboratory features in our area. Mean age was 37.5 years and 86% of patients were females. The etiology could be determined in 67.5% of cases: sarcoidosis (20.6%), drugs (18%), streptococcal infection (16.3%), tuberculosis (6.3%), pregnancy (1.9%), Crohn's disease (1.3%), Behçet's disease (1.3%), lymphoma (0.6%), adenocarcinoma (0.6%), and toxoplasmosis (0.6%). 32.5% of cases were idiopathic. We found significant differences between the different etiological factors regarding mean age, fever, joint disease, ESR, leukocytosis and serum proteins. We compare our results with those from other series and we emphasize the need for a systematic workup in all patients with EN to facilitate their etiological diagnosis.