A case of infective endocarditis caused by Streptococcus acidominimus is reported.An 81-year-old Caucasian man underwent an elective transcatheter aortic valve implantation due to his severe aortic valve stenosis. He presented to the hospital 3 weeks later with a 1-week history of fever (39ºC) that did not resolve following a 3-day course of azithromycin and a 5-day course of ciprofloxacin. Three sets of blood sample cultures were taken. Empirical antimicrobial treatment was initiated to target gram-positive and gram-negative microorganisms and consisted of vancomycin 1 g intravenous (i.v.) every 12 hours and imipenem-cilastatin 500 mg i.v. every 6 hours. After 48 hours, the blood culture was positive for S. acidominimus. The strain was sensitive to ampicillin, cephalosporins, tetracycline, and vancomycin. It was resistant to penicillin, macrolides, trimethoprim-sulfamethoxazole, and fosfomycin. Transesophageal echocardiography showed a small mobile vegetation attached to the anterior mitral valve leaflet, along with mild mitral regurgitation. The patient was diagnosed with native mitral valve infective endocarditis, and imipenem-cilastatin was discontinued. The patient showed clinical and laboratory improvement during his 2-week hospitalization. A peripherally inserted central catheter was put in place, and the patient was discharged on i.v. vancomycin to complete a total of 6 weeks treatment, after which the infection resolved.An 81-year-old man diagnosed with mitral valve endocarditis caused by S. acidominimus was successfully treated with vancomycin.