BackgroundCaptive Andean bears (Tremarctos ornatus) develop a distinct alopecic syndrome of unknown aetiology.Hypothesis/ObjectivesTo describe the histological features of healthy Andean bear skin, to define the clinical and histopathological features of Andean bears with signs of alopecia, and to propose an aetiopathogenesis.AnimalsEighteen healthy Andean bears housed in 12 European zoos and 13 Andean bears with mild to severe alopecia housed in nine European zoos.MethodsTwo surveys describing signalment and clinical features of affected bears; follicular density was measured in a single healthy bear using a dermatoscope; cytological samples were collected by tape stripping from two healthy and three alopecic bears; skin biopsies were collected for histological evaluation from healthy and alopecic bears; immunohistochemistry (CD3, AE1/AE3 cytokeratins) was performed when lymphocytic inflammation was observed.ResultsThe syndrome is an acquired, slowly progressive alopecia. Bears are otherwise healthy. Histological features include a dermal inflammatory infiltrate composed of T lymphocytes and eosinophils; atrophy of hair follicles at the level of or below the isthmus, and lymphocytic infiltration of hair follicles and the epidermis. Multinucleated giant cells were present in the outer root sheaths of hair follicles in five bears.Conclusion and clinical importanceAndean bear alopecia syndrome is an acquired, progressive alopecia with histological features consistent with a lymphocytic immune‐mediated reaction directed against follicular sheaths and the epidermis. Trigger factors have not been identified. Further studies are indicated to define the features of this multifactorial syndrome.