Abstract Background Infective endocarditis is a relatively common disease in a cardiologist’s daily practice. Nowadays more detailed information about pathogens is provided to us by diagnostics such as MALDI Biotyper Massa Spectrometer. We present a case of endocarditis lenta in which Streptococcus sinensis was identified in the Netherlands for the first time. Case summary A 58-year-old man was admitted with high suspicion of endocarditis lenta complicated by severe kidney dysfunction and anaemia. He was treated with penicillin and gentamycin. Transthoracic echocardiogram revealed a large vegetation at the mitral valve and MALDI Biotyper Massa Spectrometer (Microflex) revealed S. sinensis as the pathogen. The patient refused to receive blood transfusions or surgery. Due to cerebral infarction with haemorrhagic transformation, the patient died 8 days after admission. Discussion Streptococcus sinensis was described in Hong Kong for the first time and is associated with endocarditis in rheumatic heart disease. To our knowledge, this is the first case reporting a fatal outcome of endocarditis due to this bacterium in the acute phase. In this case, late discovery, disease severity, and under treatment all contributed to the poor outcome. We want to share the knowledge on the existence of this bacteria.