SummaryA golden retriever dog was evaluated for cranial abdominal organomegaly. Clinical investigation found concurrent splenomegaly, anaemia, thrombocytopenia, hypoalbuminaemia and hypocholesterolaemia. Cytological evaluation of splenic aspirate samples identified a population of atypical, erythrophagocytic, mesenchymal cells. Due to the patient’s signalment, clinicopathological abnormalities and splenic cytological findings, the dog was suspected to have haemophagocytic histiocytic sarcoma. Splenectomy with splenic histopathology was performed to confirm the diagnosis. Histologically, granulomatous splenitis with erythrophagocytic macrophages was identified; a cause for splenitis was not identified. The dog was clinically diagnosed with reactive haemophagocytic syndrome secondary to splenitis. The patient clinically decompensated a month postsplenectomy and was euthanased.