Leishmaniasis and leprosy comprise the group of granulomatous diseases. Although both diseases have a known occurrence in Brazil, their concurrent presence is rare, and few cases have been reported in the literature. We report the case of a 46-year-old male patient co-infected with leprosy and mucosal leishmaniasis. Examination revealed an ulcerated lesion on the nose and a lesion with a granulomatous surface on the palate, in addition to spots on the arms and legs. Histopathological analysis of the oral cavity specimen was suggestive of mucosal leishmaniasis, although no amastigotes were identified. A new biopsy was taken to collect material for PCR and the remaining was subjected to hematoxylin-eosin (H&E) staining. Finally, the diagnosis for Leishmania braziliensis was positive. A skin biopsy suggested the diagnosis of leprosy on the right leg and left knee by Fite-Faraco staining (Ziehl-Neelsen). The results obtained indicated simultaneous infection with M. leprae and L. braziliensis. After diagnosis, the patient was treated for co-infection and has been under follow-up for 2 years without signs of recurrence. The diagnosis of leishmaniasis/leprosy co-infection is challenging because of the broad clinical spectrum. Few cases have been reported in the literature and the dentist may play an important role in its detection. (AU)