While leprosy is usually a chronic disease, leprosy reactions may lead to acute problems. These reactions most often occur after initiation of therapy, but can also develop before treatment. Leprosy rarely presents with a reaction. We describe a German patient who presented in this unusual way in order to demonstrate the various tools used to confirm the diagnosis. A young German woman suddenly developed progressive functional loss of the left hand and within a few weeks an increasing number of erythematous macules and nodules appeared. Histological examination of a skin biopsy revealed tuberculoid granulomas, some located around small nerves; acid-fast bacilli were detected microscopically and DNA from Mycobacterium leprae was identified by polymerase chain reaction in the biopsy and a nasal swab; serological tests were positive. The disease was classified as borderline lepromatous leprosy. The acute neuritis followed by skin lesions represented a leprosy type 1 reaction in which the immune system reacts to bacilli previously unrecognized in nerve tissue, both in nerve and skin.