Summary Eosinophilic synovitis (ES) is a rare disease described in human and veterinary medicine. Only three cases have been reported in the horse. A case of tarsocrural synovitis in an Hispano-Arabian gelding is presented in this report. The patient presented with severe joint effusion and lameness of the right tarsocrural joint on admission. Synovial fluid analysis revealed an increased WBC of 12800 leukocytes/microliter with 76% of eosinophils. Lavage of the diseased joint and medical treatment with antibiotics and non-steroidal anti-inflammatory drugs produced remission of the clinical problem.