A case of febrile ulceronecrotic Mucha‐Habermann's is presented. This disorder is a severe form of pityriasis lichenoides et varioliformis acuta (PLEVA) characterized by the sudden eruption of diffuse coalescent ulcerations associated with high fever. In the present case the disease was preceded by the milder typical form of PLEVA. Histologically a leukocytoclastic vasculitis was seen in addition to the usual lymphocytic perivascular and lichenoid infiltrate. During the course of the disease the patient developed an interstitial pneumonitis which resolved concomitantly with the cutaneous lesions. Adenovirus type II recovered at the height of the illness from the patient's urine may have etiologic implications in the pathogenesis of the diseas