Erythema nodosum is an acute inflammatory dermatosis characterized by painful nodules which are generally symmetrical and non ulcerative and are mainly located to the extensor surface of the lower legs. The nodules, due to septal panniculitis, are often accompanied by fever and resolve without permanent sequelae. Arthralgia occurs in more than 50% of patients and begins during the eruptive phase or precedes the eruption by 2-4 weeks. Erythema nodosum is presumed to be a hypersensitivity reaction and may occur in association with several systemic diseases or drug therapies, or it may be idiopathic. The most common cause of erythema nodosum is streptococcal infection in children and streptococcal infection and sarcoidosis in adults. Peak incidence occurs at age 18-34 years. Age and sex distributions vary according to etiology and race; women are affected more often than men. It is possible to distinguish between an acute and a chronic form of erythema nodosum; in the acute form, an early stage and a late stage can be detected, both clinically and histologically. Laboratory and instrumental examinations to be performed in case of erythema nodosum are varied and are intended to identify any underlying trigger disease. Erythema nodosum is a self-limited disease, so the therapy is often only symptomatic. Even if the erythema nodosum quickly responds to systemic steroids, in most cases their use is not recommended, nor necessary; is usually sufficient to use NSAIDs (eg, acetyl salicylic acid, ibuprofen, naproxen, indomethacin).