Erythema nodosum migrans (ENM) is believed to represent a variant of chronic erythema nodosum; however, others consider it to be a separate clinical entity. It most commonly affects women in the third to sixth decade of life. Most cases are idiopathic, but some may be associated with streptococcal infection or thyroid disease. We present a case of ENM in a 33-year-old male patient with an erythematous, painful and infiltrated nodule on the lateral left lower leg. The lesion enlarged centrifugally, and a similar lesion appeared on the right lower leg. Both plaques exhibited a tendency to central clearing that made a peripheral ring evident. The patient was concurrently under treatment with antiviral drugs for hepatitis B infection and had an excellent response to treatment with potassium iodide. An association of ENM with the patient's viral hepatitis B could not be excluded.