A case of localized beak infection by Penicillium cyclopium in a macaw (Ara ararauna) is described. A necrotic lesion, with destruction of the corneous layer, was localized in the upper zone of the beak. Diagnosis was carried out on samples of the affected zone by direct microscopic observation, routine fungal culturing techniques, and scanning electron microscopy. Results were consistent: P. cyclopium was the only microorganism associated with the lesion site. No previous reports concerning this type of beak pathology have been found in the literature.