Background:The Harpy eagle (Harpia harpyia) is the largest raptor in the Neotropical region, distributed in low densities within primary forest habitats from southern Mexico to east-central Brazil, including Central America and Panama. Although locally extinct due to habitat degradation, human poaching and reduction of tropical forests in recent decades, some remnant populations are known to be small and isolated. Thus, information on its ecology, including infectious diseases, is critical for conservation efforts and management of populations of this emblematic species in the wild. Avian Mycobacteriosis (AM) is a chronic disease affecting a wide range of birds and mammals and clinical cases have been sporadically reported, although in harpy eagles, has not been documented. In addition, scant information exists on pathologies affecting raptors, therefore, this report expands the knowledge on infectious diseases affecting wild birds. This study describes the first case of AM in an immature harpy eagle rescued from Darien gap and presents details of the clinical manifestation of the disease and its histological findings. Case: An immature harpy eagle was presented to a rescue center after being confiscated by Ministry of Environment from a local farm in a remote region of Eastern Panama, in the Darien gap. The raptor had a history of having been kept in captivity for approximately five weeks, cohabiting with backyard poultry and fed corn, raw duck and chicken provided by farm owners. Stagnant water was offered for drinking. The harpy eagle arrived to the facility very lethargic and emaciated. Physical examination revealed damaged plumage, poor body condition and dyspnea. Complete blood count revealed anemia and leukocytosis based on lymphocytosis and eosinophilia. Biochemical profile evidenced an increased level of aspartate aminotransferase (AST), phosphorus and total plasma protein. Most remarkable radiographic findings were splenomegaly, hepatomegaly and increased opacity in kidneys, intestines, and aerial sacs. None of the other diagnostic tests performed were conclusive, like tracheal, esophageal and cloacal cultures for fungal infection and fecal exam. After one week of treatment, it showed a remarkable recovery, but at the end of the second week, declined dramatically, dying in the third week of treatment. Post-mortem examination revealed the presence of diffuse granulomas in multiple organs. Histologic examination with gram and Ziehl Neelsen staining revealed the presence of gram-positive and acid-fast bacteria, compatible with Mycobacterium-like bacilli. PCR-restriction fragment length polymorphism analysis of the hsp65, digested with BstEII and HaEIII restriction enzymes confirmed the presence Mycobacterium avium complex in tissues samples. Discussion: This is the first report of AM in a harpy eagle, presenting an extreme emaciation with dyspnea, abnormalities in spleen, liver and air sacs. Biochemical and hematological parameters revealed alterations consistent with infection and organ malfunctions in li...