Erythema nodosum refers to the development of multiple painful nodules in recurrent crops on the pretibial areas bilaterally. Sixty percent of cases are idiopathic (without apparent cause). In the other forty percent, the skin lesions are simply the cutaneous manifestations of a systemic disease. What other diseases are associated with erythema nodosum depend on the geographic area you are in. In the Midwest, streptococcal infections predominate. In Scandinavia, tuberculosis should be looked for. In the Philippines, leprosy is likely. Southwest of this country, coccidiomycosis is likely and in the Southeast, North American blastomycosis is likely. Drug eruptions to iodides, bromides, penicillin, sulfa drugs and birth control pills may be associated with erythema nodosum. This is an important disease to recognize. With appropriate therapy, the problem clears quickly.