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Background: Hemophagocytic lymphohistiocytosis (HLH) is a rare but severe and potentially fatal syndrome that is characterized by increased proliferation and activation of benign macrophages with hemophagocytosis throughout the reticuloendothelial system. This syndrome is classified as primary (genetic) or secondary when acquired in the context of infections (usually viral), malignancies, rheumatologic and metabolic diseases., Case Summary: We report a case of HLH complicating a Haemophilus parainfluenzae mitral valve endocarditis and resolving under antibiotic and surgical treatment alone. We also review other case reports of infective endocarditis associated with HLH., Conclusion: The syndrome is probably underdiagnosed. To our knowledge, this is the first report of a HLH syndrome associated with H. parainfluenzae endocarditis.