Gemella morbillorum (G. morbillorum) is part of the commensal flora of the oropharynx and intestinal tract, and on rare occasions causes infective endocarditis. A 55-year-old man with massive aortic regurgitation caused by recurrent infective endocarditis with G. morbillorum had a history of prior endocarditis caused by α-hemolytic streptococcus and multiple antibiotic allergies 5 years prior, and was successfully treated by aortic valve replacement. Almost all the reported cases of endocarditis caused by G. morbillorum have been bacteriologically cured with antibiotics and this is the first reported case of recurrent endocarditis caused by G. morbillorum in which the initial infection was bacteriologically cured by antibiotics and the secondary infection treated with valve replacement. This organism can be one of the causes of infective endocarditis and prompt surgical repair is mandatory if the infection is refractory or there is progression of congestive heart failure under antibiotic cover. (Jpn Circ J 2001; 65: 997 - 1000)