Endocarditis caused by lactobacilli is very rare and so far has been rarely published in adults with cardiac valve diseases especially after dental manipulations. Because of diagnostic and therapeutical problems we hereby report on one case of a female adolescent with Down's syndrome who did not undergo surgical correction of atrioventricular septal defect because of early development of Eisenmenger's syndrome. The onset was subacut and the diagnostic procedures were considerably delayed. Risk factors for the development of endocarditis in this case were preceding antibiotic treatments which increased the risk of selective growth of the causative germs as well as the tricuspidal valve incompetence with simultaneous pulmonary hypertension. The antimicrobial treatment was difficult due to resistance to antibiotic drugs generally applied in such cases and the restricted bacteriological diagnostic methods. Finally we had successfully administered chloramphenicol. The course was complicated by cerebral embolic events. FACIT: Lactobacillus species are facultative pathogenic which should be consideration in cases of subacute endocarditis in children and adolescents with ventricular septal defects and valve diseases. The determination of minimal bactericidal concentration of antibiotic agents and time-kill studies of combined antibiotics are recommended. For initial therapy we recommend high dose penicillin combined with an aminoglycoside. In cases of resistance chloramphenicol should be taken into account as second choice antibiotic drug. The duration of antibiotic therapy should at least over six weeks. In cases of risk systemic embolization is suspected therapy with low dose acetylsalicyclic acid or cardiosurgery should be assumed as therapeutic options.